Lightning Protection And Insulation Coordination Of Mixed-voltage Quadruple-circuit Transmission Line On The Same Tower

With the rapid development of economy and power grid construction, the resource of transmission line corridor is scarce in our country. Reference to experience of developed countries, the application of mixed-voltage quadruple-circuit transmission line on the same tower is becoming increasingly widespread. As a result of high tower and multiple circuits on a single tower, the lightning performance and insulation coordination of multi-circuit transmission line on the same tower is different from conventional single-circuit line. For example, Multi-circuit transmission line is stroked by lightning more easily because of the higher tower height; multi-circuit lightning outage at the same time may occur, which threatens the reliability, security and stability operation of power system; in order to reduce the rate of multi-circuit lightning outage, there are two different points of view about whether balanced or unbalanced insulation level mode should be used for the same voltage level double-circuit, as well as insulation coordination of the different voltage levels.Until now, lightning overvoltage and insulation coordination of mixed-voltage multi-circuit transmission line has not been fully researched in our country. And the relevant provisions of previous industry standards for single-circuit line or high-tower line are out of place. Therefore, it is necessary to start a systematically study.In this thesis, example of typical type of quadruple-circuit transmission line with Dual Voltage 220/110kV is taken out. Lightning performance is calculated and analyzed with EGM (Electro-geometrical Model) and EMTP (Elector-Magnetic Transient Program), and design principles of lightning protection and insulation coordination are proposed. Among them, improved EGM considers the earth, ground wire and all conductors as a unified whole; the use of EMTP takes the induced voltage and frequency voltage into account, and multi-surge impedance model is used to describe the multi-circuit tower.The results show that several special methods that may be used to improve lightning performance are presented, such as reducing nominal height of the tower, using negative fielding angle and setting up additional shield wires. It is better to use negative fielding angle and lateral rod to control shielding failure trip-out rate; to improve protection performance of back flashover, balanced higher insulation level mode is recommended, and setting up additional shield wires and other preventive measures should be considered; and it's proposed to take full advantage of 'the natural insulation difference', In addition, the insulation co-ordination of mixed-voltage multi-circuit line should focus on lightning protection, and should not be 'one size fits all'. Finally, from the angle of lightning protection, method of insulation co-ordination design is proposed--statistics of related parameters and a reasonable division of line segment are done firstly; insulation level and other counter-measures of back flashover are determined secondly (Taking the anti-pollution-flashover insulation level as initial value, it's necessary to determine the insulation level of relatively low-voltage line using method of addition by degree firstly, and then determine the insulation level of high-voltage line); fielding angle and other counter-measures of shielding failure are determined.