Investigation On Jump After Ice-shedding And Torsional Behavior Of Bundle Conductors

The ice coating on the transmission lines will fall off under natural conditions such as temperature rise or manual de-icing situation,which will cause a vertical vibration of the line,that is,“Ice-shedding”.It may lead to electrical accidents such as flashover,conductor burns and line trips,as well as mechanical accidents such as fitting damage,conductor rupture and tower collapse.In addition,under the combined effect of severe ice and wind,the torque may be generated on the bundle conductors due to the non-uniform ice and wind load,which causes the twisted deformation of the bundle conductors.In severe cases,it may cause torsional instability,in the case of which the sub-conductors will be twisted together and can not return to its original state,that is,the phenomenon of “Bundle conductors rolling” occurs.It may cause wear of the sub-conductors and damage of the fittings,thereby shortening the service life of conductors and fittings.Therefore,the investigations on ice-shedding and torsional behavior of bundle conductors behave great significance on theoretical and engineering practice.Firstly,based on similarity principle,a reduced-scale test model of a three-span continuous line is established.The displacement variations of the conductors are measured using monocular image recognition technology and the tension variations on conductors are recored with tension sensors.The validation of the method is verified with the test results of full-scale lines after ice-shedding.By means of the method,the non-uniform and uniform ice-shedding tests of transmission lines are carried out,and the applicability of the simplified engineering practical formula of maximum jump height of conductors after ice-shedding based on numerical simulation is verified.Based on the simulation test results after ice-shedding,the simplified calculation formula of jump height is improved,and the application scope of the formula is expanded.Considering the torsional similarity between the propotype of bundle conductors and reduced-scale model,an approximation method for reduced-scale modeling test of torsional instability and restore of bundle conductors is proposed,and a reduced-scale simulation test platform for torsional instability of twin bundle conductors under the effect of concentrated torque is estabilished.In the tests,the torsional angle of bundle conductors is measured by means of binocular image recognition technology.The validation of the method is verified with torsion test results of full-scale lines.By means of the method,the reduced-scale simulation tests of torsional instability and restore of twin bundle conductors under different parameters are carried out.The torsional collapse torque,torsional stiffness and self-restoring torque are measured,and the phenomenon of bundle conductors rolling is revealed.The effect of the loading and unloading rate of torque,initial tension on sub-conductors,layout of twin bundle conductors,spacer number and the arrangement of spacers on torsional behavior of twin bundle conductors is simulated.Using the UEL user defined subroutine in ABAQUS software,the loading of distributed torque along the line is implemented and the numerical simulation method to simulate the torsional instability and restore process of bundle conductors is proposed.By means of the method,the torsional behavior of quad bundle conductors under distributed torque is simulated and the difference between torsional behavior of bundle conductors under distributed torque and concentrated torque is analyzed.Moreover,the effect of unbalanced tension in sub-conductors,the clamping loose between spacer and sub-conductor and electromagnetic force between sub-conductors,etc.on torsional behavior is simulated,and the approaches to improve the anti-rolling ability of quad bundle conductors are analyzed.Based on the numerical simulation method to simulate the torsional instability and restore process of bundle conductors under distributed torque,numerical simulation of instability process of bundle conductors under different line structure parameters,including the type of conductors,bundle numbers,bundle spacing,span length,hight difference,initial tension on sub-conductors and arrangement of spacers,is carried out,and the torsional stiffiness and collapse torque of different bundle conductors under various parameters are obtained.Based on numerical simulation,a big sample database of collapse torque and torsional stiffness of bundle conductors under more than twenty thousands parameter combinations is carried out.Using the big sample database and BP neural network algorithm a surrogate model to quickly predict the collapse torque and torsional stiffness of bundle conductors is set up.Based on the surrogate model and particle swarm optimization(PSO)algorithm,the optimization method for the arrangement of spacers of bundle conductors is proposed.For different bundle conductor lines,using the maximum collapse torque and maximum torsional stiffness as the objective function respectively,the arrangement of spacers is optimized,and a better anti-rolling ability of arrangement of spacers obtained by optimization than that provided by the exsiting design standard is obtained.The research findings of this paper provide the important theoretical and technical support for the electrical insulation design,tower head design,and anti-rolling design of bundle conductors in ice zone,and it is of important theoretical significance and practical application prospects.