Eddy Current Pulsed Thermography for Noncontact Nondestructive Inspection of Motor Winding Defects

Abstract

Electrical rotating motor is one of kernel equipment of industrial applications. They are subjected to various thermal, environmental, load stresses that ultimately lead to failure and catastrophic accidents. Winding inter-turn fault is the most severe faults in the motors. Defects inspection is of great significance to ensure safety operation and reduce downtime. In this paper, eddy current pulsed thermography (ECPT) was firstly applied to defect four types of winding defects, namely, transverse crack, slot crack, insulation breakage and insulation thinning. The mechanisms of electromagnetic induction and heat conduction in the process of ECPT are introduced. The electromagnetic fields and temperature distributions of different types of defects are simulated and analyzed through multiphysics-based models. Experiments are conducted on a winding copper bar cracks sample covered by polyimide (PI) film. The validity of ECPT is verified with the analysis of IR images and thermal responses. In order to further improve the detection capability of ECPT, signal processing algorithms such as Fast Fourier Transform (FFT) and Principal Component Analysis (PCA) are applied to enhance cracks characteristics in the original IR images by eliminating the non-uniform heating effect. Obtained results demonstrated that ECPT is a feasible and effective approach for motor winding defects inspection.