Analysis And Research On Electro-thermal Coupling Of Preground Wire Port Of Overhead Ground Wire Based On Skin Effect

During the operation of the overhead line,there is a disconnection fault,resulting in a regional power outage.The reason is the broken wire or broken strands of the pre-twisted wire hardware port of the overhead ground wire.Power outages will cause serious economic losses.If the wires or overhead ground wires that cross important facilities such as subways and oil and gas pipelines are broken.They may also cause secondary disasters,which are very bad in nature.The wire breakage of the overhead ground wire is concentrated at the junction of the fittings,especially the pre-twisted wire port of the overhanging wire clip,and there are often cases of wire breakage and strand breakage.So far,there is no unified understanding and measures for the ground wire breaking mechanism and response measures.In order to ensure the normal and stable operation of the power grid and reduce the number of broken wires and broken strands,this article takes overhead ground wire pre-twisted wire ports as the research object,starting from skin effect,contact resistance,and thermodynamic heat transfer.The analysis method of experiment and finite element simulation calculation is used to summarize the mechanism of the lightning conductor breaking at the pre-twisted wire port.Based on the disconnection mechanism of the lightning conductor at the overhang string at the conclusion,corresponding improvement measures or optimization schemes are proposed to reduce the risk of disconnection of the lightning conductor overhang string.Firstly,the current research status at home and abroad was investigated from the aspects of the research background of overhead ground wire disconnection,contact resistance,skin effect,and transient temperature rise of short-term high current.A dynamic calculation method of contact resistance based on the axial heat path model of the ground wire and pre-twisted contact ports was proposed.The relationship between contact resistance and temperature was calculated by combining with experimental data in the literature.Secondly,a three-dimensional electromagnetic field finite element simulation model with the contact end face and its vicinity as the research object is established.Analyzed its current density distribution and related influencing factors.Based on this three-dimensional model,by simply establishing a two-dimensional electro-thermal coupled finite element simulation model of the contact end face,the effects of different types of current,pre-stranded wire material,and different coating thickness on the transient temperature rise were studied and analyzed.A three-dimensional electromagnetic field finite element simulation model of the pre-twisted wire port of the ground wire is established as the research object,the current density distribution under different skin effect degrees is analyzed,and the relationship between the transient temperature rise and the current density under the condition of large current is derived.A three-dimensional finite element simulation model of the electromagnetic-thermal-solid multiphysics coupling of the ground pre-twisted wire port was established,and the current density distribution and transient temperature distribution inside the port under the action of power frequency short-circuit current were calculated.The simulation results show that the transient temperature rise at the first row of contact points in the port is higher,and a larger temperature rise occurs.The larger temperature rise makes the ground wire in the port generate additional thermal stress,which further increases its stress level.Therefore,the contact point of the pre-twisted wire and the ground wire is determined to be the most obvious bottleneck point of temperature rise,and the pre-twisted wire port has become the most concentrated location of thermal stress and mechanical stress,which is very likely to cause the risk of wire breakage.Based on the wire breakage mechanism of the pre-stranded wire port obtained in the summary,two improvements are proposed for the pre-stranded wire port in this article.One is to use a stepped pre-stranded wire port and the other is to use a pre-stranded wire without frost.