Ultrasonic Detection Of Cable Partial Discharge Based On Mach-zehnder Fiber Optic Sensor

Partial discharge(PD)process is often accompanied by acousto-optic signal generation.Compared with electrical detection methods such as partial discharge pulse current method and ultra-high frequency method,optical fiber detection is free of electromagnetic interference,simple to lay,and easy to network,which is conducive to on-line detection and has a great application prospect.In this thesis,polycarbonate(PC)rods with 30 mm length,11 mm diameter and 0.5 mm thickness were wound around the fiber based on the principle of optical interference of Mach-Zehnder to develop ultrasonic ordinary 1550 nm single-mode fiber interference sensor,polarization-preserving insensitive fiber optic interference sensor.Both sensors resonance frequency is 40 k Hz,and the corresponding fiber interference system was built to investigates the ultrasonic signal generated by the cable PD.Ultrasonic generators were used to generate 28 k Hz and 40 k Hz ultrasound to research the effects on the fiber sensing performance of the distance and the different thicknesses of silicone rubber between the sensor and the ultrasonic by using the fiber optic interference system.The results show that polarization-preserving insensitive fiber optic interference sensor and its fiber optic interference system can get response to 40 k Hz ultrasonic wave.Meanwhile,the sensing signal is increased with the thickness of the silicone rubber when there is silicone rubber between the ultrasonic source and the sensor.Two defective electrodes were fabricated: a 1 mm XLPE plate glued metal plate was used to make a parallel plate electrode,and a needle tip electrode was inserted into an insulating block 100 mm length,100 mm width,2 mm thickness to make a silicone rubber electrode with a joint burr model.Build a test platform for discharge detection,and use a fiber optic interference system to detect the ultrasonic discharge.The test proves that when the voltage of the test transformer rises to 10 k V and the PD Base II partial discharge detector detects 1000 p C discharge,the ultrasound signal of the parallel plate electrode discharge detected by the optical fiber system is around 26 k Hz,41 k Hz and suspected 56 k Hz.