ABSTRACT
Overhead Transmission Lines are not insulated but is carrying current at extremely high voltage. It is suspended from the transmission towers through insulator that also work as protectors. Electrical design of overhead insulators dictates the number of insulator discs, vertical or V-shaped string arrangement and phase-to-tower clearance. The insulator must withstand transient overvoltages due to lightning and switching surges, even when insulators are contaminated by fog or in the rainy season or industrial pollution. Mechanical design focuses on the strength of the conductors, insulator strings and support structures besides tensile and oscillatory forces of the conductors. This chapter starts with different types of overhead insulators. The chapter also provides how to calculate string efficiency of overhead insulators including methods mitigation of stress on each disc of a string insulator.
