Fault Detection In Locomotive Gear By Motor Current Dual-Tree Complex Wavelet Packet Analysis

The fault detection of traction system has been a challenging problem to ensure the safety and economic operations of railway locomotives.Due to poor working conditions,frequent load changes,space limitation and dynamic action,anomalies such as pitting,wear and broken teeth sometimes occur in locomotive gears.Compared to the conventional vibration monitoring techniques,stator current-based monitoring offers significant economic savings and implementation advantages.For precise and reliable gear fault detection,the dual-tree complex wavelet packet transform is employed to analyze the locomotive traction motor current signal.The contributions and conclusions are made as follows:The formulation for the load torque has been deduced again,taking into account the real frequency components observed in the torque and vibration signals.Furthermore,the source of mesh and rotating frequency components in the stator current is analyzed.As a result,the traction motor can be considered as a torque sensor through its electromagnetic-torque estimation for torsional vibration monitoring without any extra mechanical sensor.A framework of locomotive gear fault diagnosis based on motor stator current signature analysis is established.The fault detection using current signals is a challenging task,because the fault-related features are weak and are usually modulated and masked by other high-level signals.In addition,the sophisticated signal path from gear defects to current transducer will lead to even lower signal-to-noise(S/N)ratio.The dual-tree complex wavelet packet transform(DT-WPT)maintains the traditional time-frequency localization analysis ability of the wavelet transform and exhibits better shift-invariance than the conventional discrete wavelet transform.The simulation detection shows that dual-tree complex wavelet packet transform has the characteristics such as approximate shift invariance,anti-aliasing property and inhibits energy leakage effectively.Fine frequency resolution may be achieved and gear fault feature can be extracted accurately via DT-WPT analysis of motor current.Based on the investigations mentioned above,a sensorless fault diagnostic approach for locomotive gears based on DT-WPT of traction motor current is presented.The proposed method was effectively applied to the operation tests of 30t axle load freight locomotives and the faults of locomotive gear were diagnosed successfully.