Optimal arrangement of the angle rings is an important part in EHV or UHV transformer’s main insulationstructure design. In this paper

multi-objective optimization algorithm

particle swarm optimization（PSO）algorithmand finite element sub-model calculation technology are used to optimize the arrangement of the left/right angle ringswith maintaining the original number and thickness of the angle rings and the arc radius unchanged. During the opti-mization process

the minimum insulation margin along the electric fluxlines in each evaluated oil clearance is select-ed as the objective function of optimization. The purpose is to make the insulation margins along the direction of theelectric fluxlines as close as possible. After optimization

the minimum insulation margin floating range of each eval-uated oil clearance becomes smaller

and the minimum insulation margin of the entire end insulation improves.