Influence of water and defects on abnormal temperature rise of composite insulator

•In this paper, the influnce of both water and defects on the abnormal temperature rise of composite insulator is studied.•The grating detection system for the temperature rise of composite insulator’s surface is set up. And the temperature rise of composite insulator before, after water immersion, and after water immersion and drying are accurately measured.•The internal defects of composite insulator are clearly detected by the phased array ultrasonic testing system. And the phased array ultrasonic recognition model for internal defects of insulator is proposed.•The transverse anatomical test of composite insulator is carried out to verify the results of the temperature rise test and the phased array ultrasonic testing test.