Non-destructive optical diagnosis of thermal deterioration for coil insulator in low-voltage induction motors

Novel non-destructive diagnostic apparatus using an optical fiber sensor was developed to predict a residual life of an aged low-voltage induction motor. This diagnosis is simple and easy, and its procedure is only measuring the optical reflective absorbance of an insulating resin. The diagnostic sensor consists of two plastic optical fibers (one is for the light transmission, another is for the light reception), a plastic optical coupler, two kinds of light emitting diodes (LEDs) as light sources, and an optical power meter as a detector, so it is very compact and lightweight (less than 2 kg). The aging of an insulating material could be estimated by using an intrinsic diagnostic curve, which is obtained by an accelerated heating test. We applied this diagnosis to predict residual lives of low-voltage induction motors used in elevators.