Study On Dynamic Responses Of Iced Transmission Line After Ice-shedding And The Mechanical De-icing Method

Ice-shedding from transmission lines under certain conditions may cause verticaljump and horizontal swing of the lines, and in turn may lead to flashover, trip, burningof conductors if the clearance between any two different phase conductors and/orbetween a conductor and a ground wire during vibration is smaller than the tolerableinsulation distance. It also may cause some mechanical problems such as rupture ofconductor and hardware fittings, failure of tower bolt or even collapse of the tower,which severely jeopardizes the safe operation of the high voltage transmission line.Therefore, the studies on the dynamic responses of transmission lines in ice zones afterice-shedding and de-icing of iced conductor behave great significance on theoretical andengineering practice.Firstly, the numerical simulation method of ice-shedding of iced conductor isinvestigated by finite software ABAQUS. Through setting the material to be ‘NoCompression’, a cable element with perfectly flexible in bending and torsion, which isused to simulate the conductor, is obtained. The static load generated by the ice accretedon the line and the dynamic loads induced by the ice-shedding from the electric lines aresimulated by means of the modification of the density and the gravity acceleration ofthe lines. The ice-shedding of an ice-shedding simulation test is numerically analyzed todemonstrate the efficiency of the presented method.The dynamic responses of typical section of500kV transmission tower-linesystem after ice-shedding are numerically investigated comprehensively in this thesis.The finite element models, including transmission towers, conductors, ground wires,insulators and spacers, of the transmission tower-line system are created inABAQUS/CAE. The stress distribution of the tower-line system under ice load and thedynamic responses of towers and electric lines after ice-shedding are obtained. Theresults indicate that the transmission tower-line system is safety. Moreover, throughcomparing the results of tower-line system with transmission line model, it is shownthat the deformation of tower have little effect on the jump height or horizontalamplitude of conductor after ice-shedding.The dynamic responses of transmission line with different structure parameters indifferent ice-shedding conditions are then numerically simulated, and the effects ofvarious factors, including number of spans, ice-shedding rate, span length, ice thickness, wind speeds, elevation difference, suspension length, conductor type and number ofsub-conductors on the maximum jump height and horizontal amplitude of the lines afterice-shedding are investigated. It is shown that the maximum jump height and horizontalamplitude of the lines after ice-shedding go up with the increases of the span length andice-shedding rate, and change very small with number of spans, elevation difference,suspension length and number of sub-conductors. A linear relation between themaximum jump height of a line after ice-shedding and the sag difference between twostatic states before and after ice-shedding, and a linear relation between the maximumhorizontal amplitude of the line after ice-shedding and the wind swing difference beforeand after ice-shedding are obtained according to the analysis on the numerical results.Based on the two linear relations, the simplified formulas for the jump height andhorizontal amplitude of electric lines with odd number of multi-spans after ice-sheddingare suggested for the design of the transmission lines in ice zones.The numerical simulation method of mechanical de-icing is investigated, andaccreted ice on the electric line is modeled as a separate pipe-beam element in parallelto each cable element by means of common nodes. The porous elastic constitutivemodels, in which the temperature and porosity are taken into account, are used todescribe the behavior of the ice accreted on conductors, and the tension failure criterionis employed to identify broken ice in the simulation of de-icing process. The usermaterial subroutine VUMAT of ABAQUS software is developed to describe theconstitutive relation of the ice and delete the broken elements. A large number ofde-icing scenarios are studied with the variables including ice porosity, temperature,number of spans, span length, ice thickness and different amplitudes of shock-loads,based on which the effects of adjacent span and insulator strings on the rate of de-icingare analyzed and discussed. The results indicate that the constitutive behavior of glazecan be described by elastic model because its porosity is very small and has small effecton its mechanical behavior, and the behavior of hard rime should be described by elasticporous medium model. The process of de-icing after loading is affected obviously by allthe above parameters except temperature. The obtained numerical results provide areference for the design of de-icing technique in practice.A mechanical de-icing device to remove the ice on quad bundle conductor isproposed. The de-icing device can be used to replace some of the spacers or all thespacers in a span, and it has the advantages of economy, safety, etc. The de-icingprocesses of iced quad-bundled conductor with the de-icing device are numerically studied with the variables including opening displacement of the de-icing device, thenumber of installed de-icing devices on the line, span length, ice thickness and numberof spans, based on which the potential of the new mechanical de-icing device isdemonstrated. The obtained numerical results provide a reference for the design andrealization of the mechanical de-icing device.