Gas-insulated transmission line (GIL) is a kind of power equipmentdeveloped for ultra-long-distance and large-capacity underground transmission lines

which is widely used all over the world. Compared with gas insulated switchgear (GIS)

due to the large total amount of insulating gas inside the GIL and the complex installation environment

the leakage may cause a great impact on the environment pollution and the safety of the power system. In China Sutong UHV GIL utility tunnel project

the total amount of SF

6

is about 750 t. In this paper

through the research and comparison of three leak detection methods

namely local binding method

overall buckle cover method and helium leakage detection method

and for the requirement of extremely low leakage rate of different types of UHV GIL

we have researched the detection methods

test devices and key parameters of local hardened buckle cover and dynamic helium mass spectrometer leak detection

which has been applied to the detection of the 20-meter-long UHV GIL. We propose a high-precision and quantifiable helium leak detection method using in the type test and routine test. The test results show that the minimum effective leak detection rate of the method can reach 1×10

-8

Pa·m

3

/s

which can be used as a basis for further improving the gas leak detection rate in the f

uture.