PSI - Issue 14

Vamsi Inturi et al. / Procedia Structural Integrity 14 (2019) 937–944 Vamsi, Sabareesh, Vaibhav/ Structural Integrity Procedia 00 (2018) 000–000

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was observed that combination of vibration and temperature data yields better result than vibration data alone. Peng and Kessissoglou [12] combined vibration analysis and wear debris analysis to detect the gear faults in a worm gear of a single stage gearbox and observed that the wear debris analysis provides additional information about the modes of failures. Loutas et al. [13] combined vibration, acoustic emission and oil debris analysis techniques in order to diagnose the faults in a single stage gearbox. Wavelet analysis was used for feature extraction and the extracted features were classified by independent component analysis (ICA). In this study, two CM techniques, namely, vibration analysis and acoustic signal analysis have been combinely implemented. The acquired data is filtered to eliminate the noise present in the raw signal and then EMD analysis is performed to elicit the IMFs. Various statistical features are extracted from the IMFs and the most significant features are identified using decision tree algorithm. Further, the features are classified into healthy and faulty by SVM algorithm.

List of Abbreviations HSS

High Speed Stage

F1 F2 F3 F4

50% Faulty (Gear tooth root crack) 100% Faulty (Gear tooth root crack) 25% Faulty (Gear tooth chip) 100% Faulty (Gear tooth chip)

ISS LSS

Intermediate Speed Stage

Low Speed Stage

EMD Empirical Mode Decomposition IMFs Intrinsic Mode Functions

SVM Support Vector Machine

2. Experimental Procedure 2.1. Experimental setup

The test rig consists of lab scaled model of a wind turbine gearbox which includes a three-stage parallel spur gearbox having overall speed ratio as 48:1. The gearbox consists of three stages namely, high speed stage (HSS), intermediate speed stage (ISS) and low speed stage (LSS). Each stage of the gearbox contains a pinion and gear held by a shaft. Two deep grove ball bearings are used to brace the shaft. The generator is replaced by a 1-hp synchronous, three-phase AC motor to drive the input shaft (HSS) of the gearbox. The maximum speed of the motor is 1440 rpm and the speed is regulated by programmable variable frequency drive (VFD). Jaw coupler is used to couple the input shaft of the gearbox and the motor shaft. Heavy gear oil (80W-90) is used as lubrication oil to lubricate the mating components of the gearbox and the applied lubrication is of free wet type, refer Fig 1. Two piezoelectric accelerometers (one tri-axis & one uniaxial) are used to acquire the vibration response and two microphones are used to acquire the acoustic signal information. Accelerometers are stud mounted on the bearing housing and the microphones are positioned over the bench top cover. All the responses are recorded at a sampling frequency of 16 kHz. Sensors are in turn connected to a data acquisition (NI-DAQ) hardware. LabVIEW accompanies the hardware with the computer and further post processing is done using MATLAB software. Additional details about the experimental test rig are provided in the Table 1 and the positioning of the sensors is illustrated in Fig. 2. As the HSS is rotating at higher operational speeds than other stages of the gearbox, the HSS components have higher chances of failure. Therefore, the HSS pinion has been chosen as target component. The gearbox is operated at 50% of the maximum speed (720 rpm) of the motor and the response is recorded in the form of vibration and acoustic signals.

2.2. Simulation of faults

It was reported that, a gear crack or tooth breakage might yield to fatal failures and hence detecting them at their nascent level of propagation is a vital task to ensure the safety of the gearbox [5]. Typically, tooth root crack evolves from the point of largest stress which is reported at the fillet region of the gear tooth root [4]. Hence, two local gear faults, namely, gear tooth root crack and gear tooth chip are considered in the present investigation. The crack (axial direction) is seeded at the root of one of the teeth of the pinion using wire cut Electro Discharge Machining (EDM).