The Study Of On-line Supervision In Squirrel Cage Induction Motors With Broken Bar

With the development of modern science and technology, electric machines play a more and more important role in modern industrial plants. The risk of machine failing can be remarkably reduced if normal service conditions can be arranged inadvance. In other words, one may avoid very costly expensive downtime of plant by proper time scheduling of machine replacement or repair if warning of impeding failure can be obtained in advance.In this paper, the research situation currently of the broken rotor bars diagnoses in asynchronous motor is discussed, which utilize the spectral components of the stator current, with comparing the characteristics of some detection methods. Based on the study of the principle in magnetic forcing, the sidebands associated with motor faults are deducted. For amplitude of the sidebands around the power fundamental component is so feeble to be detected when motor is incipient fault, Adaptive Notch Filter is introduced to deal with it. Adaptive Notch Filter is applied to weaken the fundamental in the stator current spectral components based on the elements of an algorithm called LMS. The emulation by Matlab presents the reliability and accuracy of it. The comparison of the spectral components using FFT algorithm is then made between the filtered and unfiltered stator current. The results indicated the f 1 frequency component is significantly reduced by Adaptive Notch Filter when the useful information is clear out otherwise it is incipient.In view of entire diagnosis system,hardware of the lower position machine through current transformer gather stator current signal. After filter circuit and enlargement circuit it put the signal of appropriate frequency to deliver PIC's A/D port to complete signal gathering. it delivers the signal on PC machine by PIC through RS232 at the same time. In PC, the data receive module receive lower position machine data real-time.In software aspect,in PIC with running rate quicker assembly language we write signal gathering,A/D conversion processing,Correspondence control program.In PC, compiles with the Delphi language. The communication manner use MSComm control to visits the PC machine serial interface.PC control interface has the data receive and the graphic display and the processing function.It operates simply and has the practical value.