.500/220kv Pressure Four-back Line Lightning Mixed With The Tower

By the continuous increasing demand of electric power in our country, the design of multi-circuit lines in the same tower is used more and more popularly in the power system network construction. The multi-lines transmits more power than the single-circuit lines, so that it takes up an more important place in power system. Because the towers of the multi-circuit lines are much higher than normal towers, they are struck by lightning easily, so the lightning protection problem is more serious than traditional towers of the same voltage rank. The calculation and analysis on the lightning protection performance, insulation coordination and other influence facts for four-circuit lines with mixed voltage ranks is not enough till present. It is quite necessarily to start researching on this domain.Lightning shielding failure and back flashover are the main reasons for lightning flashover on HV and EHV lines. The calculating methods in the OVERVOLTAGE PROTECTION STANDARD are wrote for normal single-circuit lines, but not for the multi-circuit lines. The exactness lightning protection performance parameters on multi-circuit lines couldn't be got by such means. So that new models and methods for such calculation should be adopted.Examples of two types of tower used in practiced four-circuit lines with mixed voltage ranks of 500kV and 220kV are took out in this thesis. Electric Geometry Method is used in the calculation on shielding failure flashover performance of such four-circuit lines. Not only the shielding contribution of shielding lines to Phase conductor is considered, but also the contribution between each line and the ground to Phase conductor is done. So the result calculated is close to the fact. In the calculation of bake striking performance, multi-surge impedance model is used to describe the multi-circuit lines tower. It is calculated particularly that the critical current required for back flashover of this nulti-circuit lines under different resistance values and phase conductors sequence. A conclusion is concluded from the result of this calculation as following. The lightning protection of 500kV lines is effected little by the resistance value, and the current for back flashover is large under various condition. But the resistance has a great impact on linghtning protection of 220kV lines, whose current for back flashover declines fast with the increasing of the resistance. Based on the back flashover analysis of this multi-circuit lines, under different conditions of various resistance value and various insulation coordination according to different resistance value, the critical current for back flashover of 500kV and 220kV lines is calculated. According to the result calculated, the value of resistance is divided into several groups: lower resistance, medium resistance and high resistance. The most suitable insulation coordination solution for every group is presented. The recommendatory insulation coordination takes full advantage of protection given by 220kV line where first flashover occurs to 500kV lines, and the lightning flash-over rate of 500kV lines is reduced as much as possible. Finally, several improved solution for lightning protection of this lines is discussed in this thesis. Through calculation, when the value of tower resistance to the ground is large, the current for flashover of 220kV lines couldn't be increased by adding a shielding line, but it can be done well by adding a coupling ground line. From the conclusions above, the final project of lightning protection and insulation coordination is given out in this thesis.