ABSTRACT
Corona is produced due to ionization of air, surrounding the conductor of overhead transmission lines, which causes non-sinusoidal voltage drop accompanied by power loss and is undesirable and uneconomical. Sag and tension, the vertical bending in shape of the conductor due to its weight, are related to laying of transmission line to accommodate the change in length due to differential temperature and heat generation. In addition, ice- and wind-loading functionally increase line weight and, along with thermal loading on the conductor, cause additional line sag or stretching. The amount of sag is a function of the conductor size, material and span distance. To satisfy the National Electric Safety Code, minimum mid-span ground clearance is required for a particular voltage level for transmission and distribution of electricity. A Sag Template is a very important tool with the help of which the position of towers on the profile is decided so that they conform to the limitations of vertical and wind loads on any particular tower and minimum clearances. This chapter deals with corona and sag.
