Optimization Design And Experimental Study Of Flexible Ultra-High Frequency Sensor For Partial Discharge Of Transformer

Power transformer,as one of the core equipment in power system,has the function of power transmission and voltage conversion.However,the internal insulation structure of the transformer is complex and the voltage span is large.It is vulnerable to temperature,electric field,mechanical and other factors that lead to insulation failure.Therefore,the research of transformer insulation monitoring has important academic significance and application value to ensure the safe and stable operation of power grid.Combined with the existing transformer fault diagnosis methods,ultra-high frequency(UHF)method is widely used due to its high sensitivity and strong anti-interference ability.However,the existing UHF detection method mainly uses rigid UHF sensor design to detect electromagnetic waves,they are vulnerable to the limitations of the installation location and size and the complex structure of the transformer,which will lead to the sensor performance and installation structure cannot be balanced.Therefore,this paper studies the propagation characteristics of UHF signal of transformer partial discharge(PD)by combining electromagnetic field simulation technology and finite-difference time-domain method.Then,this paper combines microwave and antenna theory,flexible antenna technology and signal processing technology to design a flexible UHF antenna suitable for the complex structure of transformer.In order to reduce the waste of resources caused by the repeated design of the sensor and improve the utilization rate of the sensor.Finally,transformer PD test platform is built to verify the performance of the flexible UHF antenna.This paper includes the following main contents:Firstly,according to the principle of PD electromagnetic wave induction,the relevant parameters of UHF sensor induced electromagnetic wave are analyzed theoretically.The propagation characteristics of PD UHF signal in transformer high voltage bushing are studied by using the finite difference time domain method.The amplitude and spectrum characteristics of electromagnetic wave signal in transformer oil tank,bushing flange,middle and top are analyzed,and the attenuation characteristics and propagation characteristics of electromagnetic wave signal in the propagation process are analyzed.It provides a theoretical basis for the optimization design and installation position selection of the flexible UHF sensor.Then,the traditional bowtie antenna is optimized and designed.Based on the exponential gradient microstrip balun structure and flexible antenna technology,a flexible bowtie antenna is designed.After adding the balun structure and flexible bending design,the size of the butterfly antenna is reduced by 40.9 % compared with the traditional butterfly antenna,and the mass is also greatly reduced.The changes of return loss,voltage standing wave ratio and pattern of flexible bowtie antenna under different bending conditions are analyzed by electromagnetic simulation software HFSS.The simulation results show that the flexible bowtie antenna still has good performance after flexible bending.Finally,the transformer PD test platform is built and two artificial insulation defect models are designed.Through the comparison test between different sensors and the bending test of the flexible bowtie antenna,the bending and detection performance of the flexible bowtie antenna is verified.According to the simulation of electromagnetic wave signal propagation characteristics of transformer bushing and the related test of UHF sensor,the packaging scheme of flexible bowtie antenna at transformer bushing is proposed.The test results show that the flexible bowtie antenna has good bending performance and can be effectively applied to the detection of PD UHF signal at the transformer bushing.