Detecting loose stator wedges in large motors

This paper presents test results obtained from studies aimed at determining whether the acoustic method, a nondestructive test technique based on the use of transient stress waves, can be used to detect the loose stator wedges. During the detection, mechanical impact is applied on the wedges and the responses are recorded by a microphone. Frequency analysis is performed in order to provide a description of the signal in frequency domain. It is shown that characteristic frequency in acoustical spectrum is the key to detecting loose stator wedges. Results also show that amplitude of the characteristic frequency increases corresponding to the looseness of wedges. Besides analysis of the test results, this study successfully introduces a thin plate resonator model for analyzing the response of a loose wedge when an impact is performed. The value of characteristic frequency is calculated for better interpretation of the detection results