Tilted Fiber Bragg Grating Twist And Vibration Sensors And Their Applications For In-filed Power Monitoring

As the basic industry for economic development,the safety and stability of the power industry is closely related to national economic security,people’s daily life and social stability.In the power system,transmission lines and transformers are two very important parts.Due to long-term operation and force majeure in nature.Power transmission cables will wear or even break due to changes in their own shear stress.Power transformers will have abnormal vibrations on the surface of the cabinet due to internal core and winding failures,which will seriously affect the safety of the power system.In order to avoid the huge economic loss caused by transmission cables and transformers,it is necessary to develop effective monitoring instruments.The optical fiber sensor uses optical signals as the transmission medium,which can realize real-time,high-sensitivity sensing and long-distance signal transmission to the external measured information.In addition,the optical fiber sensor has the advantages of anti-electromagnetic interference,good insulation,fast response speed,corrosion resistance and easy multi-point networking.It provides a new direction for the development of modern sensing technology and is suitable to power transmission systems with limited traditional electronic sensors.According to the actual needs of power grid monitoring,this thesis develops a surface plasmon resonance fiber twist sensor for transmission lines and a multi-point fiber vibration sensing network system for ultra-high transformers.(1)Surface plasma resonance optical fiber twist sensor for"air-liquid"dual media measurement.An optical fiber twist sensor based on surface plasmon resonance(SPR)excitation and able to operate both in gaseous and liquid media is proposed and demonstrated.The use of a gold-coated 37.5~°tilted fiber Bragg grating allows to generate two windows of cladding mode resonances,providing surrounding refractive index sensitivity in two different external media.The relative optical power of the SPR mode in each case exhibits a linear response to the twist angle of the fiber from 0~°to 90~°,as well as from 90~°to 180~°,as a consequence of the polarization dependency of these sensors.The results show sensitivities of 1.15%/~°and 1.22%/~°with the sensor working in air and liquids respectively,being suitable for deformation measurement and structural health monitoring applications.(2)Construction of multi-point optical fiber vibration sensing network and system for ultra-high power transformer.A fiber-optic vibration sensing system was successfully installed on the 500k V three-phase transformer of the#2 main transformer in Yunfu Wolong Substation,Guangdong.Six sensors are installed in the same position of the three phases of ABC power transformer,a total of 18sensors are installed to monitor the health of the transformer in real time.The sensors used in the system are based on a cantilever structure.The time-frequency signals collected through coherent demodulation are analyzed,the amplitudes of the 100Hz,200Hz and 300Hz components are analyzed under normal working conditions.The vibration intensity of each phase of A,B,and C three-phase transformers will be in an amplitude space,and the fluctuation amplitude for long-term operation is limited.By monitoring the amplitude of the vibration frequency component of the transformer,health problems of the transformer structure can be predicted.