Adeline Bourdon

On the use of the Instantaneous Angular Speed measurement in non-stationary mechanism monitoring

Power transmission faults are one important cause of machine downtime many production activities are working to prevail. Vibration monitoring tools have achieved this role on the assumption that the stationary condition hypothesis is maintained. Several industries, including wind energy production, are however demanding to observe mechanical or electrical rotating components behaviour at variable speeds. Instantaneous angular speed measurement has been recently proven able to detect localized faults in bearings using only an encoder close from the source of the defect. This paper presents the results obtained from a large span experiment on a 2MW wind turbine. The uniqueness of the sensor used to monitor the whole line shafting along with the continuous non stationary conditions are so many difficulties cumulated on this attempt. Two basic signal processing tools are theoretically defined and experimentally applied in an original way on the Instantaneous Angular Speed measurement to efficiently tackle these practical issues.Copyright

Electrical Modeling for Faults Detection Based on Motor Current Signal Analysis and Angular Approach

Recently, Motor Current Signal Analysis (MCSA) appears as an effective tool for fault diagnosis in rotating machinery and proved to be sufficient for detecting localized mechanical faults in electromechanical systems operating in stationary conditions. In the case of non-stationary conditions, speed variations must be distinguished from angular velocity perturbation caused by the presence of a defect. In the framework of diagnosis of rotating machinery, angular approaches are well suited to make monitoring resistive to speed disturbances. This paper proposes a reformulation of the MCSA associated with angular approach in modeling multiphysic behavior. The resulting model described in this paper can be used to investigate of the influence of the Instantaneous Angular Speed (IAS) variations on the electrical responses of the whole rotating system.

Instantaneous Angular Speed Monitoring of a 2MW Wind Turbine Using a Parametrization Process

One cannot but notice that a variable speed wind turbine utilizes the available wind resource more efficiently than a fixed speed wind turbine, especially during light wind conditions. Most wind turbines are equipped with doubly fed induction generator, thereby allowing them to keep on producing while the speed varies over a wide range. This enhancement forces the monitoring methods to deal with these large variations in speed and torque, since the conditions are seldom if ever stationary. In an original and inexpensive attempt to tackle this issue through angular sampling, this paper proposes to base the surveillance of the line shafting on the instantaneous angular speed variations experienced by the high speed shaft. The unsteady behaviour of these wind turbines is also a difficulty in term of long term diagnostic, since the comparison of successive measurements is usually performed under the same operating conditions. Parametrization of the indicators according to well chosen variables might bring a valuable tool regarding several aspects. A long term experimental study carried over a 2MW wind turbine will be presented as a first application, and will be used to dress an interesting diagnosis on another wind turbine.

Reconstruction of the Instantaneous Angular Speed Variations Caused by a Spall Defect on a Rolling Bearing Outer Ring Correlated with the Length of the Defect

In the framework of monitoring of rotating machinery, this paper proposes a simple signal processing tool to reconstruct the Instantaneous Angular Speed (IAS) variations caused by the presence of spalled bearing. This tool is applied to signals obtained on a specific test bench. Associated with an angular sampling, the analysis of these variations can identify the length of the defect whatever the mode of operation, particularly in non-stationary operating conditions in rotation speed.

Modelling Roller Bearing Dynamics Inducing Instantaneous Angular Speed Variations

Modelling the dynamics of roller element bearings has been used to explain the interactions between localized faults and their impact on the measurable quantities representing the dynamic behavior of the system e.g. acceleration. Most part of the models describes the non-linear contact of roller bearing normal forces by means of Hertz Theory. Recently, analysis of the Instantaneous Angular Speed (IAS) has been proven to effectively detect bearing mechanical faults and it has shown to be an advantageous tool for non-stationary machinery surveillance. Mechanical analysis implies that rotating speed variations are due to torque variations. However, the phenomena describing how dynamic interaction of bearing components induces tangential forces generating angular periodic disturbances to the shaft speed, have not been discussed at all. In this work an original formulation to induce tangential forces to the shaft due to the bearing components dynamics is presented. The roller bearing model is based on Hertzian contact, localized faults can be added and the analysis is suitable for simulation of non-stationary conditions.

Current Signal Analysis of an Induction Machine with a Defective Rolling Bearing

With the ultimate goal of rotating machinery diagnosis using Motor Current Signal Analysis (MCSA), this paper provides a coupled electro-magnetic-mechanical model of a rotating shaft supported by rolling bearings and driven by a three-phase squirreled cage motor. The modeling is based on the hypothesis that a bearing defect causes torque and then Instantaneous Angular Speed (IAS) variations associated to air-gap eccentricity of the induction machine rotor. Dynamic analysis of the multiphysic system highlights the sub-systems interactions, especially, angular periodicities and frequency modulations. The global model can be characterized by a unique set of non-linear state equations which are solved iteratively by an angle-step scheme while considering the angle-time relation. The major interest of presenting this model is that it allows to decrypt the transfer path from a small localized bearing defect until its manifestation on electrical signals. Analysis of bearing defects were performed by applying Fourier Transform on current per-phase signals.

Simplified Dynamic Model of a Wind Turbine Shaft Line Operating in Non-stationary Conditions Applied to the Analysis of IAS as a Machinery Surveillance Tool

Instantaneous Angular Speed (IAS) has been shown to be an alternative signal to detect bearing faults in geared systems. Detection of the presence of bearing faults in rotating systems requires understanding of the transfer way between the defect and its manifestation in the measured signal. This step is mainly performed by the development of numerical models describing the couplings between the defects and the rest of the device. To the authors’ knowledge, the majority of the models in the literature are lump parameter models, with no regard between the dynamic of the bearing and the rotational degree of freedom of the shaft. The influence that the dynamics of a faulted bearing has over the rotating shaft leading to IAS variations has been presented in a previous work. This influence has been introduced by means of a roller bearing model which dynamics, modified by the defect, introduces torque perturbations to the shaft. The aim of this paper is to couple the faulted bearing model to a multiple gear stage simplified wind turbine transmission. The model is built with a classic finite element approach and is suitable for the test of non-stationary simulations. First results show bearing faults are detectable in different locations of the geared system by the measurement of IAS. Even if experimental validation have not been yet performed, numerical results appear very promising to deepen the understanding of the IAS variation phenomena.

Dynamic Behavior of Very-High Speed Rotors at Non-stationary Conditions

Speed reducers with input shafts spinning at very high speeds (up to 42 000 rpm) are generally associated to electric motors, which are more and more used especially in the automotive field, in order to bring the rotational speed to the most efficient window. Accurate modeling of those rotating machinary behavior is crucial to improve product reliability and to prolong machinery life. Many studies are conducted with an imposed angular speed, which is in most of the cases considered as constant or, in best cases, which follows a given variation law. In this paper, the study is performed with no assumption on the rotational speed. A variable driving torque is induced to the input shaft and the instantaneous angular speed (IAS) is deduced from the dynamic problem coupled to an angular approach. As a result, the IAS takes into account not only the induced torque perturbations but also the periodic geometry of the whole structure (e.g.: bearings and gears). The aim of this work is to extend the existing model based on the Finite Element Method by introducing an enhancement of the gyroscopic effect matrices without any assumption on the spinning speed. This model will lead to the introduction of coupling between the flexural and torsional degrees of freedom as well as to a non-linearity in the modeling of the studied system. The aim is to improve the accuracy of simulations for the rotor dynamics in non-stationary conditions especially when getting through critical speeds.

Detection of Bearing Spalling Faults Using IAS Monitoring System - Experimental Studies on the Influence of Operating and Environmental Parameters

Experimental works carried out in recent years have demonstrated the feasibility of detecting a bearing fault through the spectral analysis of the Instantaneous Angular Speed (IAS) in the angular domain. Since these works have been carried out on complex mechanical systems (automotive gearboxes, vehicle wheels, wind turbines), neither the influence of operating parameters, nor the influence of structural parameters over the observed angular speed variations have been clearly identified. However, the implementation of effective tools for condition monitoring prospects requires a deep understanding of these interactions. In this regard, a test bench has been designed to allow defective bearing monitoring through IAS observation of a simple shaft running under varying loads and speeds, the system being simple enough to be easily described in various kind of mechanical or phenomenological models. The aim of this paper is to present a better understanding of the relationships between the speed variation induced by the monitored fault, the structural response and the observed phenomena. In the first part results obtained for a healthy bearing will be analyzed. These initial results serve as a reference for analysis of the results obtained with bearing defects. Coupled with dynamic modeling, they will also highlight the existence of a low frequency torsion mode. The results of this first part also highlight the wider interest of the IAS analysis for the study of rotating systems. In a second part, the measurements are performed with bearings having spalling type defects on their outer ring. The aim of this section is to estimate the influence of operating conditions on IAS monitored indicators. All these results will provide further phenomenological explanations of coupling between bearing fault and rotating speed.