Transmission and Distribution 10EE53 10. Give the list of supporting structures and the main components used in overhead transmission line. December 2015 In order to determine the conductor load properly, the factors that need to be taken into account are: Weight of conductor itself. Weight of ice or snow clinging to wire. Wind blowing against wire. The maximum effective weight of the conductor is the vector sum of the vertical weight and the horizontal wind pressure. It is very important to include the most adverse condition. The wind is considered to be blowing at right angles to the line and to act against the projected area of the conductor, including the projected area of ice or snow that may be clinging to it. Economic design dictates that conductor sag should be minimum to refrain from extra pole height, so provide sufficient clearance above ground level, and to avoid providing excessive horizontal spacing between conductors to prevent them swinging together in mid-span. Conductor tension pulls the conductor up and decreases its sag. At the same time, tension elongates the conductor, from elastic stretching, which tends to relieve tension and increase sag. The elastic property of metallic wire is measured by its modulus of elasticity. The modulus of elasticity of a material equals the stress per unit of area divided by the deformation per unit of length. That is, since where stress per unit area in pounds per square inches σ= = conductor tension in pounds T A = actual metal cross section of conductor in square inches The resultant elongation of the conductor due to the tension is e Page 22
Transmission and Distribution 10EE53 10. Give the list of supporting structures and the main components used in overhead transmission line. December 2015 In order to determine the conductor load properly, the factors that need to be taken into account are: Weight of conductor itself. Weight of ice or snow clinging to wire. Wind blowing against wire. The maximum effective weight of the conductor is the vector sum of the vertical weight and the horizontal wind pressure. It is very important to include the most adverse condition. The wind is considered to be blowing at right angles to the line and to act against the projected area of the conductor, including the projected area of ice or snow that may be clinging to it. Economic design dictates that conductor sag should be minimum to refrain from extra pole height, so provide sufficient clearance above ground level, and to avoid providing excessive horizontal spacing between conductors to prevent them swinging together in mid-span. Conductor tension pulls the conductor up and decreases its sag. At the same time, tension elongates the conductor, from elastic stretching, which tends to relieve tension and increase sag. The elastic property of metallic wire is measured by its modulus of elasticity. The modulus of elasticity of a material equals the stress per unit of area divided by the deformation per unit of length. That is, since where σ= stress per unit area in pounds per square inches T = conductor tension in pounds A = actual metal cross section of conductor in square inches The resultant elongation e of the conductor due to the tension is Page 22