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Measurement of Compressive Internal Stress in GIS Epoxy Composite Using Ultrasonic Longitudinal Critically Refracted Wave Method

Basin insulators are significant components in gas-insulated metal-enclosed switchgear (GIS). The internal stress in basin insulators can cause cracks, and other insulation faults. In this research, a method for measuring the internal stress based on the ultrasonic longitudinal critically refracted (LCR) waves is proposed. Some epoxy specimens were manufactured, of which the material and the manufacture process were the same as the 252 kV GIS basin insulators. An ultrasonic LCR waves system was set up to investigate the internal stress of epoxy specimens under the compression in the range of 0-50 MPa. 2.5 MHz frequency can provide a better performance than 0.5 MHz frequency when the LCR wave method is used. The results show that the LCR propagation time is linearly decreased with compressive stress increasing, and the acoustoelastic coefficient is calculated to be -4.950. The probe placement configurations are proposed in measuring the circumferential stress and axial stress in the basin insulators.