| Power cable is an important transmission equipment in power system.The safe and stable operation of cable is of great significance to power system.Vibration analysis plays a unique role in state diagnosis of power equipment because it has no direct electrical connection with power equipment and can be monitored online in real time.However,the theoretical system of the vibration mechanism of power cable is still not perfect and the progress is relatively backward.It is difficult to provide sufficient theoretical and data support for the state diagnosis of power cable based on vibration analysis method.Therefore,this paper takes underground cable as the research object,and studies the vibration model and characteristics of cable.The main contents are as follows:(1)A mathematical model of cable vibration is established based on D’Alembert principle and Hamiltonian principle respectively.The vibration equation contains the fourth partial derivative of space variable x and the second partial derivative of time variable t;The vibration mathematical model is solved by mode superposition method,and the mathematical expression of cable vibration displacement in time and space is obtained,which lays a theoretical foundation for the study of vibration characteristics.(2)Study cable vibration characteristics under the action of electromagnetic force.Firstly,the analytical formula of the electromagnetic force received by the cable is derived.Secondly,the mathematical expression of the vibration displacement of the cable under the electromagnetic force excitation is obtained by theoretical calculation.The fundamental frequency vibration characteristics of the cable are analyzed.The vibration response of the B-phase cable is calculated by taking the 220kV three-phase single-core cable as an example.Finally,considering the slight variation of cable phase spacing caused by electromechanical coupling,the parametric vibration equation under electromechanical coupling is derived.Linzteider-poincare perturbation method is used to analyze the multi-frequency vibration characteristics of the cable when there is a specific relationship between the natural frequency of the cable and the frequency of the power supply,and the vibration mechanism of the cable is enriched.(3)Based on COMSOL multi-physical field simulation software,a three-dimensional finite element model of 220kV three-phase single-core crosslinked polyethylene cable was established.The electromagnetic field distribution and fundamental frequency vibration characteristics of the power cable were simulated and analyzed,and the validity of the theoretical model was verified.Secondly,the power cable vibration signal acquisition experiment is carried out to verify the correctness of the three-dimensional finite element model of the cable.Finally,based on the finite element model,the frequency of the power supply is parameterized,and the multi-frequency vibration characteristics of the cable under electromechanical coupling are verified.(4)Three different states of the cable are simulated.Firstly,the three-phase load is unbalanced,and the variation trend of the three-phase cable vibration signal with the single-phase load current is simulated.Secondly,the vibration characteristics of cable under different insulation aging states are obtained by simulation.Finally,the distribution law of electromagnetic field and vibration characteristics of cable before and after damage are compared and analyzed.It is found that there are great differences in the vibration amplitude and frequency of cable vibration characteristics under different states,which provides a certain feasibility for the application of vibration analysis method to the online monitoring of cable status. |
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