Method of sizing the sheds of post insulators in view of improving their electrical performance under cold atmospheric conditions

Among the solutions proposed to improve the dielectric behaviour of post insulators covered in ice in periods of melting, there exists a simple solution which consists of modifying the insulator geometry by increasing the diameter of certain sheds by the addition of auxiliary sheds. The preliminary tests carried out in the laboratory on the prototype post insulators show a slight improvement of the voltage behaviour in a period of melting compared to the standard insulators, and that there is a lack of information concerning the use of the extensions to the sheds. This article thus proposes a method permitting the determination of the number, the position and especially the adequate dimensions of the auxiliary sheds employed for improving the dielectric behaviour of standard 735 kV post insulators covered in ice. This method is based on experimental studies of ice accumulation and on the 3D numerical modelling of the voltage distribution and electric fields along the insulators covered in ice.