Study of auto-reclosure strategy for 110kV overhead-underground system in Kunming power grid

In recent years, the proportion of under-ground cables in power gird has increased. More and more overhead - underground hybrid lines have come out. It is necessary to do further research on the problem that whether auto-reclosure should be put into operation on overhead-underground hybrid lines. In this paper, the phase matrices of overhead- underground hybrid lines are derived at first, then the capacitive effect is analyzed and voltage transfer coefficient of hybrid lines is calculated. Taking one typical hybrid line as example in Kunming power grid, detailed models of it was built up in PSCAD/EMTDC. A large number of simulations for various reclosure angle were performed. Factors affecting the over-voltage caused by auto-reclosure are analyzed. And the mid-time method for judging the fault region is presented. The theory reference that whether reclosure should be put into operation on 110 kV overhead-underground hybrid lines of Kunming power grid is provided.