Transmission and Distribution 10EE53 Thus, the portion OP of the conductor is in equilibrium under the tension T at P. the weight wsacting vertically downward, and the horizontal tension H. In the triangle shown in Figure 2, ds represents a very short portion of the conductor, in the region of point P When is increased by ds the corresponding x and y are increased by dxand dy, respectively. Hence, Figure 1. Conductor suspended between supports at same elevation. Integrating both sides gives Therefore, Page 12
Transmission and Distribution 10EE53 conductor too tight, which causes the conductor to be overstressed and stretched when the heaviest loading takes place and the normal sag after this loading becomes excessive. Then the excessive sag needs to be pulled out of the conductor, a process that also causes the conductor to be overstressed on heaviest loading. This process of overstressing and pulling up may cause the conductors, especially the smaller ones, tohe broken. This can be eliminated by measuring the line tension more accurately. A transmission line conductor at a river crossing is supported from two towers of height of 40m and 30m respectively above water level. The horizontal distance between the towers is 300m. If the tension in the conductor is 1500 kg, find the clearance of the conductor at a point midway between the supports. Weight of the conductor is 0.8 kg/m. Assume bases of the tower to be at the water level. December 2013 catenaryMethod A span of conductor with two supports at the same level and separated by a horizontal distance L. Let ‘0’ be the lowest point on the catenary curve and ‘l’ be the length of the conductor between two supports. Let ‘w’ be the weight of the conductor per unit length, ‘T’ be the tension of the conductor at any point ‘P’ in the direction of the curve, and H be the tension at origin 0. Further, let ‘s’ be the length of the curve between points 0 and P, so that the weight of the portion s is ws. Tension T can be resolved into two components, T the horizontal component and T,, thc vertical component. Then, for equilibrium, Thus, the portion OP of the conductor is in equilibrium under the tension T at P. the weight wsacting vertically downward, and the horizontal tension H. In the triangle shown in Figure 2, ds represents a very short portion of the conductor, in the region of point P When is increased by ds the corresponding x and y are increased by dxand dy, respectively. The factors affecting the sag of a conductor strung between supports arc: 1.Conductorloadperunitlength. Page 24
Transmission and Distribution 10EE53 a resulting burst of noise. the limiting environmental design factor. State the various properties of an insulator. Give the list of important insulators and make the comparision of pin and suspension type insulators. Dec2015 Succinctly put, corona is a luminous partial discharge due to ionization of the air surrounding a conductor caused by electrical overstress. Many tests show that dry air at normal atmospheric pressure and temperature (25 °C and 76 cm barometric pressure) breaks down at 29.8 kV/cm (maximum, or peak, value) or 21.1 kV/cm (rms, or effective, value). There are always a few free electrons in the air due to ultraviolet radiation from the sun, cosmic rays from outer space, radioactivity of the earth, etc. As the conductor becomes energized on each half cycle of the ac voltage wave, the electrons in the air near its surface are accelerated toward the conductor on its positive half cycle and away from the conductor on its negative half cycle. The velocity attained by a free electron is dependent on the Intensity of the electric field. If the intensity of the electric field exceeds a certain critical value, any free electron in this field will acquire a sufficient velocity and energy to knock one of the outer orbit Page 30