Lightning Impulse Voltage-time Characteristics of Extra-high Voltage Insulator Strings in High Altitude Area

The lightning impulse voltage-time characteristics of insulator string are crucial for lightning protection design of transmission lines and PGLPD design.The lightning impulse voltage-time characteristics of 14 and 28 units XP-70 suspension insulators as well as composite insulators whose dry arcing distances were the same as 14 units XP-70 suspension insulators were experimentally investigated in the National Engineering Laboratory(Kunming) for UHV Engineering Technology.Conclusions can be drawn as follows: the lightning impulse characteristics of insulator strings are not related to materials but related to the dry arcing distances;when porcelain insulator strings flashover,the arc climbs along the insulators from the high-voltage side to the earth side,and jumps over the last 2~5 units insulators of the earth side;when composite insulator strings flashover,the arc burns in a discharge channel between the high-voltage side and earth side in the air,probably with the existence of second discharge channel.