The insulation material used in power equipment will bring some small defects after long-time operation.It is useful to find these defects promptly through ultrasonic detection and ensure the safety of the power equipment.According to ultrasonic testing requirements for internal defects of solid insulation materials

the applicable frequency for ultrasonic probe is determined by comparing the sensitivity and attenuation of multiple sensors with different center frequency. The main factors affecting the detection sensitivity are analyzed in this paper. The ultrasonic automatic detection system which can accurately get defect appearance is designed

and the ultrasound imaging method to get the defect appearance is proposed based on echo characteristic parameter analysis. To verify the practicability of the detection method

the ultrasonic testing system is used to test some artificial defects in epoxy. The results show that the system can accurately identify internal void with diameter greater than 130 μm.Furthermore

it can give the 2-dimensional appearance of the internal electrical breakdown channels and also its spatial position information. It seems that the ultrasonic detection method can be applied to instruct the insulation diagnosis for different power equipment.