Research On Discharge Mechanism And Monitoring Technology Of Bird Damage On Overhead Transmission Lines

Overhead transmission lines play the role of power transmission in the power system.They are often erected in sparsely populated areas.Therefore,bird activities are more frequent near overhead transmission lines,which may harm the normal operation of overhead transmission lines.The harmful bird activities are called bird damage.Bird damage will bring serious losses to the safe operation of the power system and the development of the national economy.Therefore,it is of great significance for the safe operation of the power system to study the discharge mechanism of bird damage on overhead transmission lines and study the monitoring device according to the discharge mechanism.Bird damage can be divided into bird droppings flashover,bird nesting fault,bird predation fault and bird flight fault.Among them,bird droppings flashover is the most important reason of bird damage discharge on overhead transmission lines.Bird droppings flashover can be divided into flashover caused by bird droppings falling near the insulator and flashover caused by bird droppings polluting the insulator.This article studies the two situations of bird droppings flashover.Aiming at the mechanism of bird droppings flashover,based on related theoretical studies,this paper established an AC 110kV overhead transmission line model in ANSYS Maxwell finite element simulation software according to the principles of electrostatic field calculation and finite element method calculation.And then this article simulated the changes in the electric field distribution near the insulator when bird droppings fall near the insulator and the changes in the electric field along the insulator shed when the bird droppings pollute the insulator.The simulation results show that when bird droppings fall near the insulator,an air gap will be formed between the insulator and the metal fittings at the high and low voltage ends of the insulator,and bird droppings will distort the electric field near the insulator,which caused the voltage in the air gap to exceed its breakdown voltage and eventually forming a flash.When bird droppings pollute the insulator,bird droppings may form a dry band on the surface of the insulator shed or short the insulator shed,so that the electric field distribution of the polluted insulator shed will be greatly distorted,which will eventually cause the flashover discharge of insulator.Aiming at the monitoring of bird droppings flashover,in view of the imperfect current monitoring technology of bird droppings flashover caused by the falling of bird droppings,this article established the models of bird droppings falling in EMTP-ATP and ANSYS Maxwell according to the mechanism of flashover discharge and simulated the change of the fault phase current and the electric field near the ground when the falling of bird droppings caused flashover.A comparative analysis was made on the monitoring difficulty of the two kinds of faulty electrical quantities,and finally the change of the electric field near the ground was selected as the monitoring quantity of the bird dropping discharge.The field mill electric field instrument was selected as the monitoring device for the change of the ground electric field.Since bird dropping flashover may occur in DC transmission lines and AC transmission lines,this article has improved the field mill electric field instrument that can only monitor the DC electric field.According to the electrostatic field principle and Gauss's theorem calculation of the electric field,the feasibility of the field mill electric field meter to measure the AC electric field was verified.Based on the calculation results,this article designed and established the circuit structure of the improved field mill electric field instrument in Multisim and achieved the monitoring of flashover caused by falling of bird droppings by simulation.