Ultrasonic nonlinear characterization of interfacial pressure in 110 kV integral prefabricated cable intermediate joints

The interface pressure between the cable accessories and the cable insulators plays a decisive role in the insulation characteristics of the accessories and the long-term reliable operation of the cable. A non-destructive testing method for joint interface pressure based on ultrasonic nonlinear effects is proposed in this paper. Considering the rough contact interface between the cable body and the accessories, a finite element simulation rough contact model of stress field sound-field coupling is constructed by using points with Gaussian probability distribution. Based on this model, first, the differences in echo signals in the time domain and frequency domain at different positions of the cable accessories, as well as the differences in time domain and frequency domain under different interface pressures at the same position, are analyzed. Second, the functional relationship between interface pressure and nonlinear parameters is fitted. Finally, a nonlinear ultrasonic test platform is built to measure the interface pressure at different positions of the cable intermediate joint. The test and simulation results show the same regularity in the time domain and frequency domain of the echo signal, and the nonlinear parameters increase with increasing interface pressure. The test results show that the detected nonlinear parameter is around 7.46×10⁻³ (with an error range within 5.80%), corresponding to an interfacial pressure of 0.21 MPa; and around 6.38×10⁻³ (with an error range within 7.60%), corresponding to an interfacial pressure of 0.16 MPa. The nonlinear parameter can characterize the magnitude of the interfacial pressure at different locations, thus verifying the validity of the simulation fitting function relationship and providing a new approach for measuring the interfacial pressure of cable accessories.