Minimum number of good (healthy) porcelain or glass insulator units in a string for live work

This paper deals with matters that impact the dielectric status of porcelain and glass insulators in a string containing broken and/or defective units that will be exposed to switching overvoltage. Flashover voltages are shown to depend on the position and number of defective units in the string. Complete understanding of all aspects of these issues is essential prior to working on a string of insulators containing defective units. Definitions of insulator defects are proposed for the special application to live working.