Cause of the tripping operation always happened in Yushu area from 330 kV Yushu project.It’s a big risk for Yushu area to have a reliability of power supply.On the other hand

in order to improve the defence ability of tripping operation and direct the differential reform of external insulation of lines

we are on this study.This study is a test of installing porcelain double umbrella/magnetic composite insulators and abrogating grading ring

then do power frequency gap discharge

ray wave gap discharge and the operating wave gap discharge test on 2 254 m and 4 200 m area

and also have a study on the level of the breakdown voltage under all kinds of install ways.Then adopt Ansoft electric simulation software and ultraviolet corona test

study the effect of install and abrogate the influence of grading ring up and down on the electric field distribution.The result of the test is that voltage level at around 3%when installing porcelain double umbrella/magnetic composite insulators in 330 kV high altitude.In order to consider the construction difficulty

it is better to install the insulator on the floor.It is also better to dismantle the equalizing ring when it can’t install.