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This paper investigates the effect of the return current path on the impulse characteristics of practical tower footings. A new circular ring electrode system is used as a return electrode for measuring the impulse response of earth electrodes. Initial measurements and computer simulations show that this system makes the current flow radially away from the electrode and dissipates more evenly in the...
In this work, the results of an experimental study of the impulse characteristic of practical ground electrodes consisting of horizontal conductors of various lengths, a grounding grid and full-scale tower footings are reported. These electrodes are installed at an outdoor test site having nonuniform soil, with equipment facilities for generating low- and high-magnitude impulse currents. The tests...
In recent years, uprating of existing overhead power line has become a popular option for electric utilities to address increasing demand for power. Uprating overhead line by increasing voltage allows considerable increase in power transfer capability. This paper initially examines technical issues and conventional methods of uprating the voltage of overhead transmission lines. It then considers a...
While uprating an overhead line to a higher voltage level, it is often difficult to achieve the required clearance level for the uprated structure. Use of Transmission Line Arresters (TLAs) is an effective technique in controlling overvoltages and thereby, achieving the required clearance margin. In this paper, suitability of this technique in reducing the clearance margin is discussed. A case study...
This paper presents a comparative lightning performance study conducted on a 275 kV double circuit shielded transmission line using two software programs, TFlash and Sigma-Slp. The line performance was investigated by using both a single stroke and a statistical performance analysis and considering cases of shielding failure and backflashover. A sensitivity analysis was carried out to determine the...
The voltage rating of overhead lines is determined by a combined consideration of the stress applied to the line and its electrical strength. In this investigation, the voltage uprating of an existing `L3' 275 kV transmission line to 400 kV is explored. Minimum air clearances for 275 kV and 400 kV lines are first reviewed and the IEC recommendations for insulation coordination were considered. The...
This paper investigates the effects of earth wire isolation on tower base voltages at a single tower of an overhead transmission line. Computation studies on a generic tower line were carried out. Various models developed to represent transmission lines including earth wires, phase conductors with different scenarios of fault locations were simulated using 'CDEGS' for direct lightning strikes to earth...
A new technique for the calculation of the surge impedance of high-voltage towers is presented. The tower is represented by a four-terminal network for which the surge characteristics are determined by solving the transmission-line equations. The boundary conditions of voltage at the top and base of the tower are determined using a numerical solution of the electromagnetic field on a physical model...
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