| With economic growth,the consumption of electricity is increasing day by day,and the requirements for power quality are getting higher and higher.As the main part of power transmission,cables are indispensable for the stable operation of power systems.At the same time,long-distance,large-scale power transmission is the main trend of future grid development,so the demand for high-voltage cable accessories is increasing.Cable accessories can not only realize the connection between cables,but also an important part of the connection between cables and other electrical equipment.The structure of the cable accessory is complicated,and its normal operation is closely related to power grid security.After analyzing the main faults in the power grid,it is found that the faults caused by cable accessories account for more than 65%.Study the distribution of electric field and temperature field inside the terminal,and provide a theoretical basis for the early diagnosis of terminal internal defects by analyzing the occurrence mechanism of terminal defects.It is of very important engineering significance for the timely detection of cable terminal failures and the maintenance of the safe and stable operation of the power system.In this thesis,taking a 220 k V cable terminal as experimental model,based on electromagnetic field,heat transfer and fluid field theory to establish the electromagnetic-heat-fluid coupling field simulation model of the high-voltage cable terminal.Then the accuracy of the model is verified by comparing the simulation data with the field measurement data.Simplified calculation of the heat generation of the porcelain sleeve type cable terminal,and the main way of heat generation inside the terminal is obtained.Firstly,the influence of water ingress defects on the stable operation of the terminal is analyzed,and the distribution law of the internal temperature field and electric field of the terminal under water ingress defects is studied.On this basis,the influence of insulation aging defects caused by the water inflow of insulating silicone oil on the stability of the terminal is studied.By studying the influence of moisture content on the dielectric loss factor of the insulating oil,the temperature field of the electric field inside the terminal when the insulating oil is aging is analyzed.The results show that the internal water ingress of the terminal and the aging of the insulation will cause local heating on the external ceramic sleeve surface of cable terminal,which makes the distortion of the field strength inside the cable terminal more obvious.In severe cases,it may cause breakdown of the weak insulation material inside the terminal.Finally,study the case of terminal oil leakage defects and analyzes the causes of the defects in the terminal.Design simulation experiments based on oil leakage defects,simulate the electric field,temperature and temperature gradient distribution of terminal oil leakage defects under different operating conditions.Analyze the temperature rise of the cable core and the field strength distortion during oil leakage.The results show that the surface temperature rise of the terminal at the oil leak is not obvious,heat will accumulate in the inner cable core,and the field strength distortion in the cavity caused by the oil leak is serious.High temperature and high pressure will increase the probability of insulation breakdown and aggravate insulation aging.The experimental results further study the possible consequences of terminal defects,and provide a theoretical reference for the failure analysis of cable terminals. |
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