| Gas Insulated Switchgear(GIS)is widely used because of its advantages over the air-insulated electrical equipments.The number of various types of defects increases with number of operational years.GIS is an important equipmen in the power system,once a fault occurs,it is easy to cause large-scale blackouts,which will seriously affects the safety and stable operation of the power grid.Therefore,the monitoring of the operation status of GIS equipment is becoming more and more important.With the development of distributed optical fiber sensing technology,some scholars gradually apply it to online fault monitoring of GIS equipment.Based on this,the principle of optical fiber distributed sensing technology is first introduced in this thesis,and then the temperature monitoring principle based on Raman optical time domain reflectometry technology and the vibration moni toring principle of phase-sensitive optical time domain reflection(Φ-OTDR)system based on Rayleigh scattering are introduced in detail.It provides a theoretical basis for temperature monitoring and vibration monitoring of GIS equipment based on optical fiber distributed sensing.In order to predict the temperature rise of the GIS contact,a 3D model of a 252 kV three-phase box-type GIS with disconnect switch is established by using multi-field coupling of electromagnetic-heat transfer-flow field in this thesis.First,the loss of each part is calculated according to the electromagnetic field theory,and then the loss is brought into the heat transfer-flow field as a heat source,and finally the temperature distribution of GIS is calculated.By changing the ambient temperature,current carrying capacity,contact resistance and other conditions,the temperature distribution of the GIS is calculated,and the relationship between the maximum temperature rise of the contacts and the corresponding maximum temperature rise of the shell,the current is obtained.Based on the obtained data,an empirical formula for predicting the maximum temperature rise of the contact was fitted,and then the formula is preliminarily validated based on the simulation results under different initial conditions and the measured GIS temperature.If the optical fiber is laid on the GIS shell,and then the shell temperature is measured by the optical fiber distributed sensing system,the temperature of the contact can be predicted based on this formula.In order to analyze the difference between the vibration signal of the two cases of loose bolts and misalignment of the guide rod at the connection of the GIS shell and the vibration signal of the normal operation,a 3D model of a 252 kV three-phase sub-box-type is established and a modal analysis is carried out on the model in the solid mechanics field in this thesis.Then the first 20 orders natural frequencies are obtained,and the representative sixth-order mode shapes are obtained,and it is confirmed that the model will not have resonance when different forces are applied.By applying different loads and changing the parameters of the model,the time-domain signals and frequency-domain signals of the vibration acceleration of GIS shell with the state of no fault,bolts loose of different number or different cases of conducting rod misalignment are solved in the solid mechanics field.The results reveal that when there is bolt loosening defect in GIS,the change of acceleration is small,but the ratio of acceleration amplitude to DC component of different frequency components changes greatly;when the guide rod misalignment defect occurs in GIS,the acceleration changes significantly,and the ratio of acceleration amplitude to DC component of different frequency components changes greatly.If the optical fiber is laid at the connection of the GIS shell,the magnitude and amplitude of the vibration frequency of the shell are measured by the optical fiber distributed sensing system,and the defects of bolt looseness and guide rod misalignment can be judged from the changes of different frequency components and amplitudes. |
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