Tri-post spacer is the key insulation support component of EHV and UHV gas-insulated transmission line (GIL)

and its mechanical reliability is directly related to the safe operation of the GIL. In this paper

the principal stress distribution and mechanical reliability of the tri-post spacer in 1 100 kV GIL are systematically analyzed with consideration of the thermal expansion

electromagnetic vibration and conductor deflection. The main conclusions obtained are as follows: The maximum tensile stress and compressive stress of the tri-post spacer at no load current are located at the lower post and the post-insert boundary

which are 2.37 MPa and 9.02 MPa respectively. It is found after comprehensive considering the influence of thermal expansion and pipeline vibration that the tensile stress is are located in the abdomen of the spacer and the boundary of lower posts

and the maximum value is 16.6 MPa. In case of conductor deflection due to assembly error

the tensile stress concentration at the boundary of the post opposite to the deflection displacement increases. The results above can provide theoretical support for improving the reliability of GIL tri-post spacer.