Up until now several methods of improving the lighting performance on overhead lines have been discussed. In most cases,these methods are adequate.However,there are cases where the qequired earthing arrangments cannot readily be applied,ie,in poor soil or rocky terrain etc. In such cases,use is made of Transmission line Surge Arresters. The application,ie,the number and positioning of TLSA is a complex subject ,with many parameters to be taken into consideration.Therefore,this can realistically only be done with the aid of modelling software such pictuer.However. What follows is a description of basic principles and application.
Initial designs were based on metal oxide surge resistors connected across the transmision line insulator,but in series with an air gap.The introduction of polymer-housed arresters has made the direct application of the TLSA(without air gaps) easier from an installation point of view.as well as from a safety consideration.