Dynamic Analysis of Multi-span Overhead Electric Transmission Line Considering Induced Ice Shedding

摘要

Overhead transmission lines in cold regions are prone to atmospheric icing hazards.Sudden ice shedding from overhead lines may cause serious electrical faults,such as flashover and short circuit due to insufficient clearance among ground wires,conductors and the earth,and mechanical incidents,such as strand(s)and cable breakage,clamp slippage,insulator rupture and cross-arm and tower deformation,due to large amplitude vibration,unbalanced loads and transient tension of conductors and ground wires.The Finite Element(FE)method is the main way to study the dynamic effects of ice shedding on line components,because of the limitations of analytical methods and physical tests.In early FE studies,ice shedding was modeled by suddenly releasing lumped ice masses from the conductors or overhead ground wires,where the ice shedding amount and location were predefined,and no extra ice deposit(located on other spans for example)was shaken off during the whole cable/line vibration process.However,in reality,more ice deposits may detach from the conductors after the initial ice shedding event.What we call induced ice shedding occurs when the resultant of adhesive force between the cable and the ice deposit and cohesive force within the ice deposit is exceeded by the ice deposit weight and inertia force resulting from the dynamic response of the line.The induced ice shedding will cause the mass,stiffness and damping of the dynamic system to vary with time,leading to a different dynamic response than if there is no further ice detachment.In this study,firstly,the induced ice-shedding effect is modeled in the form of a user-defined subroutine in the FE analysis of a multi-span transmission line section,where the relation among adhesive force,cohesive force,gravity and inertia force is considered to obtain the force balance/imbalance condition that will define whether or not subsequent shedding occurs after the triggering event.Secondly,a comparison of the results obtained without considering induced ice shedding indicates that the dynamic response changes significantly,and the previous method may underestimate or overestimate the threats of ice shedding.Then,the influential factors,initial ice shedding amount and initial ice shedding locations,are studied and the dynamic characteristics of the response are obtained and compared.This paper provides a powerful tool to significantly improve the accuracy of FE simulation of ice-shedding effects on overhead lines,which is important to ensure the mechanical safety and serviceability of transmission lines in cold regions.