Insulator and clearance requirements in overhead line transmission systems without shield wires

This paper theoretically examines the required insulation lengths and clearances in 400 kV overhead line systems when not making use of grounded shield wires as lightning protection. The influence of lightning strikes on the insulator flashover rate in the system is investigated based on dynamic transmission line simulations of a 400 kV section in PSCAD/EMTDC. The performance of the system without shield wires is considerably deteriorated if no steps are taken to increase the insulation level of the system. However by considerably increasing the insulator lengths and clearances in the system the performance can be improved.