In the temperature rise test of 1 000 kV UHV AC GIL prototype

the temperature of an expansion joint used to compensate the expansion deformation due to thermal expansion and cold contraction is significantly higher than that of other parts of a pipeline. In order to study the characteristics of loss distribution in different parts of the GIL expansion joint

a three-dimensional finite element simulation model was established based on the GIL compound pull rod type expansion joint. Considering the harshest condition（operating current returns 100% through the pipe shell）

the influences of the permeability of bellows materials

the size of the central conductor and operating current value on expansion joint loss were analyzed. Results show that the return current flowing through the bellows（about 3.19% of the total current） is the main reason for the loss of the bellows. The increase of permeability of some bellows caused by manufacturing will increase the loss of bellows shell. Increasing the outer diameter of the center conductor will significantly reduce the loss of the conductor itself

but has little effect on the loss of other parts of the expansion joint. Changing the operating current value can change the overall loss

however does not change the proportion of the loss of each part of the expansion joint. In order to further reduce the loss of the bellows

the measures of limiting the current by unilaterally adding half-conductive layer or insulating layer are put forward

which not only reduces the loss significantly

but also eliminates the potential safety potential of the suspension potential.