Voltage Distribution Effects of Non-Uniform Units in Suspension Strings

10 unit and 22-unit cap-and-pin type insulator strings are used in 154 kV and 380 kV Turkish national power transmission systems. Turkish national electric power transmission utility staff prefer replacing the damaged units by stronger fog-type ones to minimize the transient outages resulting because of the insulation problems at the lower and upper units in the string. However, it is obvious that such a replacement changes the voltage distribution of the string composed of identical units. This change depends on the several parameters. This study presents the simulation results of voltage distribution along a 10-unit suspension string and 22-unit suspension string. Studies were conducted for the strings composed of different types of units for different tower designs and different contamination cases under power frequency voltages and lightning impulse voltages.