Application of Magnetic Fields To Aid The Detection and Diagnosis of Induction Motor Drive Faults

Abstract

A novel approach to the collection of fault related data associated with induction motor drives is presented. The stator to rotor magnetic flux of an induction motor is monitored by a number of strategically positioned search coils, each wound around a single stator pole. The data collected is in the form of time records of the induced voltage in the coils and is subsequently used to form the data base for a fault detection and diagnosis strategy. Voltage waveforms obtained from a single coil and from two coils connected in series are obtained whilst the system is subjected to a range of applied electro-mechanical faults. The applied faults are applied both to the mechanical load and to the induction motor itself. A comparison is made of the efficacy of using two search coils compared to employing a single coil for fault detection. The fault related data is collected under both steady-state and accelerating running conditions. Strictly the acceleration period waveforms are non-stationary, however, since the time dependant frequency changes are relatively slow, the author applied the FFT technique to both steady-state derived data and the acceleration period derived data. Processing is carried out on both the time domain and the corresponding frequency domain data. The non-stationary nature of the acceleration period records is taken into account and the Wigner-Ville technique is employed to establish a time-frequency-distribution. Amplitude-time-frequency 3-D representations are produced, from which the amplitude versus time activity of a typical acceleration period component frequency is presented.