Optical Fiber Sensing Detection Technology For Partial Discharge Acoustic Emission In Liquid-solid Composite Insulation

Electromagnetic interference and low sensitivity low are key technical problems to be solved for the traditional acoustic method to detect partial discharge(PD). In this paper, high sensitive fiber Fabry-Perot sensors which are applied for PD acoustic emission detection in liquid-solid composite insulation are designed and fabricated, and the design methods are optimized. The characteristics of fiber sensors signals of PD detection are analysed in the experiment. The method of operating point stabilization for fiber sensor is studied. Sound field distributed in liquid insulation is analysed in electrical equipment, and fiber sensors layout scheme is presented in power equipment.Intrinsic and extrinsic fiber Fabry-Perot sensors are designed to detect acoustic generated from PD. Frequency responses are simulated and analysed for intrinsic fiber Fabry-Perot(IFPI) sensor coupling acoustics with cylinder and extrinsic fiber Fabry-Perot(EFPI) sensor coupling acoustics with diaphragm. The results show that IFPI sensor with cylinder acoustic coupler is suitable for lowfrequency vibration detection, and EFPI sensor with diaphragm acoustic coupler could be used to detect PD high frequency acoustic emission. Fabry-Perot sensor spectrum visibility affected by beam divergence, reflective surface tilt and reflectivity is analysed based on multi-beam interferometer principle. According to theory of elastic mechanics, frequency response characteristic and static pressure sensitivity of EFPI are researched, and design rules of EFPI sensor diaphragm are presented. EFPI sensors with different characteristic parameters are designed. Several types of packaging structure for EFPI sensor are designed, and sensor probes with pigtail and fiber stub are fabricated. EFPI sensors have the widening high response nearby the first intrinsic frequency because of viscous damping effect of insulating oil.A fuzzy-PID controlling method is presented to stabilize operating point in the demodulation system, which laser source is the tunable distributed feedback(DFB) laser. The operating point stability of fiber Fabry-Perot sensor is observably increased. The demodulation system with locking operating point is designed and fabricated, and the variation of operating point is less than 0.8% in the environment where temperature changes continuously from 3oC to 43oC.Acoustic-electrical PD detection system is set up, and sensitivity of EFPI sensors with different characteristic parameters is researched. It is analysed that the relations of EFPI sensor sensitivity with frequency response and static pressure sensitivity. The sensitivity of EFPI sensor is researched, which is affected by spectrum interference visibility and the position of operating point on the interference fringe. According to frequency spectrum signature detected acoustic signals by PZT and EFPI from PD different electrode model, and optimized frequency design rule of EFPI sensor is presented. Acoustic energy mean square value in frequency domain related to PD level are discussed.The same scale 3D models are set up, and the sound field distribution is analysed by the acoustic coupling filed finite element method in the liquid insulation of cable terminals and oil-immersed transformer. Solid medium could reflect and attenuate sound signals, but sound pressure is more stronger in liquid medium nearby the solid medium. The characters could provide guidance for sensor location in equipment to get higher detection sensitivity. Location plan of EFPI sensors in cable terminal and oil-immersed transformer are presented.