A new method for stator slot wedge testing of large generators

When large generators become operational, the stator bars in the slots are subjected to the electromagnetic force during normal operation. After the generators have been operating for a long time, the electromagnetic force may cause the stator bars to vibrate due to the existence of loose stator slot wedges in large generators. This leads to mechanical abrasion of the groundwall insulation and accelerates the deterioration of the generator, and can even cause generators to fail if the slot wedges are not treated. In order to ensure large generators continue working reliably, it is essential to detect loose slot wedges in the stator slots. This paper describes the modeling of slot wedges with different fixing styles in large generators to study the process by which slot wedges become loose, and also presents an analysis of the looseness of slot wedges based on their vibration characteristics corresponding to the loosening process of the stator slot wedge. Moreover, a series of tests were performed with a nondestructive detection system developed based on this analysis to check the tightness of slot wedges in the laboratory. The results showed that loose stator slot wedges of large generators could be detected either by their vibration frequency or by their displacement amplitude. This verified the correctness of the slot wedge loosening process and the validity of the detection system.