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This paper presents some mitigation solutions for improving the performance of EHV post station insulators under severe icing conditions using modified grading rings. For this purpose, numerical simulations using the finite element method (FEM), implemented by the commercial software Comsol Multiphysics, were performed, in parallel with experimental tests to study and evaluate the influence of the proposed solutions on ice-covered insulator performance during melting period. The solution proposed consists in adding a fine metallic and conductive mesh on the standard grading ring. In addition to improving the potential grading, the metallic mesh allows the grading ring to behave like a booster shed by created a large air gap under it. Experimental tests under severe icing conditions reveals that using two modified standard grading rings permits to improve maximum withstand voltage by 17% compared to the standard grading ring alone. Also, numerical simulations permits to demonstrate that increasing the diameter of the modified grading ring helps to improve both maximum withstand voltage and uniformity of potential distribution of the EHV post station insulator. The results obtained will also be useful to improve general knowledge on the use of grading rings for the EHV post station insulator under clean and severe icing conditions.