Research On Broken Wire Detection Of Prestressed Concrete Cylinder Pipe Based On Orthogonal Electromagnetic Principle

Prestressed concrete cylinder pipe(PCCP)is a high-performance composite pipe with compression resistance,impermeability and a low cost.It is widely used in largescale water conservancy projects such as South-to-North Water Transfer.The fracture of the internal prestressed steel wire is its main failure mode and causes catastrophic accidents such as pipe bursting.Aiming at this problem,the broken wire detection based on the orthogonal electromagnetic principle is deeply studied.The detection system model and boundary condition settings are established and optimized through a finite element analysis tool.The mechanism of orthogonal electromagnetic broken wire detection and the characteristics of broken wire signal are studied.The effects of edge effect,circumferential relative position of the detector and broken wires,excitation frequency and relative magnetic permeability of the wire on the characteristics of broken wire signal are analyzed,which could provide theoretical guidance for field detection and reduction of false alarm rate.The corresponding solutions are proposed for the special structures of the model and the influence of the steel cylinder structure on the simulation results is analyzed,which could provide a reference for the improvement of computational efficiency.An orthogonal electromagnetic broken wire detection system is designed and implemented.Concretely,the excitation coil and the detection coil for the diameter of 1600 mm pipe are developed.The excitation magnetic field can reach 40 Gs and the detection signal can reach the order of millivolts which could meet the system requirements.A high-voltage and high-power sinusoidal signal coil driving scheme based on sinusoidal pulse width modulation and an intelligent power module is innovatively proposed and the corresponding protection circuit is implemented,which can effectively drive the high inductance value coil with a low cost.Moreover,a data acquisition unit,a quadrature lock-in amplifier and a USB data transmission module are developed through FPGA.An experimental platform of PCCP broken wire detection is built.The variation law of broken wire signal characteristics at different excitation frequencies is verified.The experimental results show that the detection system can achieve a signal-to-noise ratio of 23 dB,which can effectively identify broken wires.Besides,an improvement scheme of experimental device is proposed,which lays a foundation for further research.