Ultrasonic nondestructive detection for defects in epoxy/mica insulation

The detection and recognition of defects in insulation is a significant investigation for insulation diagnosis. In our laboratory, an ultrasonic testing system has been developed and used for insulation diagnosis of large generators. Using this system with lower frequency transducers, experiments were performed on actual stator bars. The results showed that, the 0.5~1.2 MHz frequency transducers could be used for the manufacturing quality test of stator bars. The 0.5~0.8 MHz transducers are more effective for aging assessment of aged stator bars. They are sensitive to the degradation and the internal mechanical damages of aged stator insulation