Unshielded Transmission Lines Research Articles

Lightning Performance of Unshielded 220 kV Transmission Lines Equipped With Metal Oxide Arresters

Overhead ground wires installed on transmission lines have been proved to be effective to protect conductors from direct lightning strokes, but ground wire breakouts due to icing are frequently reported. In order to prevent electric failure accidents caused by ground wire breakouts under icing conditions, unshielded transmission lines equipped with metal oxide arresters (MOAs) whole line have been proposed in high mountainous areas. Compared with ordinary transmission lines, lightning stroke risk of unshielded lines is much higher. In order to improve the lightning performance of unshielded lines, it is necessary to obtain the essential lightning energy absorption ability of the MOAs installed on unshielded lines. In this article, simulation model of unshielded 220 kV transmission lines equipped with MOAs is built, the influences of lightning parameters, striking occurrence point and grounding resistance on the absorbed energy of MOAs are analyzed. Based on Monte Carlo method, lightning trip-out rate of unshielded transmission lines are calculated, and suggested energy absorption ability of MOAs is proposed, which can give references for the improvement of power supply reliability of transmission lines.

Lightning Performance of Unshielded 220kV Transmission Lines Equipped with Metal-oxide Arresters

Overhead ground wires have been proved to be effective to protect conductors from direct lightning strikes, but breakouts of ground wires have been frequently reported. In order to prevent ground wire breakout incidents to happen, unshielded 220kV lines equipped with metal oxide arresters (MOAs) whole line have been proposed in this paper. After cancelling ground wire, lightning strike risk of transmission lines becomes much higher. In order to improve the anti-lightning abilities of unshielded transmission lines, it is necessary to obtain the lightning energy absorption ability of these MOAs. In this paper, simulation model of MOA equipped unshielded 220kV transmission line was built, the influences of lightning parameters, striking occurrence point and grounding resistance of transmission tower on the absorbed energy of MOAs were calculated, and the suggested energy absorption ability of MOA was given, which can give references for the improvement of power supply reliability of transmission lines.

Radio frequency coupling between an antenna and two unshielded parallel wires above a metal sheet-measurement precautions

An unshielded 1 m transmission line, made of two parallel wires suspended 0.1 m above a plane metal sheet, is illuminated in the VHF and UHF bands by a log-periodic dipole array (LPDA). A network analyzer is used to measure the voltage induced at one end of the line. The measured signal is compared to the predictions of a moment method numerical analysis, using the NEC code. The measured and predicted coupling are in reasonable agreement only once two measurement precautions are taken. First, the illuminating antenna has to be well-balanced to suppress common mode radiation from the coaxial cable connecting the transmitter to the antenna. Second, an output balun must be inserted between the unshielded transmission line and the coaxial cable to the network analyzer. This is needed to prevent common mode signals on the coaxial cable from contaminating the measurements. Besides these practical steps, it is also necessary to use physical insight and high frequency circuit theory to develop a good equivalent circuit of the output balun for use in the computational model.

Use of line surge arresters for the improvement of the lightning performance of 63 kV and 90 kV shielded and unshielded transmission lines

The lightning performance of 63 kV and 90 kV shielded and unshielded power transmission lines, protected by surge arresters are considered. A specialized software package is used for the computation of the line's fast front transients. A Monte Carlo statistical method, together with a three-dimensional electrogeometric model is used to determine the lightning stroke locations. Different arrester installation configurations are analyzed and compared. The energy duties of the transmission line surge arresters are computed statistically.

A finite difference approach that employs an asymptotic boundary condition on a rectangular outer boundary for modeling two-dimensional transmission line structures

The derivation of three asymptotic boundary conditions is presented. Techniques for implementing each of these on finite difference meshes with rectangular outer boundaries are discussed. Numerical results obtained using these boundary conditions in the finite difference analysis of both shielded and unshielded transmission lines are shown. The authors present detailed convergence studies on the use of each of these boundary conditions and discuss the memory requirements of each.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Lightning Performance of Unshielded Transmission Lines

This paper presents further analyses of stodiesof the lightning performance of unshielded transmission lines by direct strokes, which were made using a developed Monte-Carlo and dynamic travelling wave program. The more important factors affecting the lightning performance as exhibited by the calculations are discussed. This led to the recognition of the basic requirements to achieve good lightning performance for such unshielded lines. A preliminary economical 33kV unshielded line design achieving these requirements is also offered.

Calculation of the Lightning Performance of Unshielded Transmission Lines

Calculation of the Lightning Performance of Unshielded Transmission Lines

Lightning Performance of Unshielded Transmission Lines

This paper presents further analyses of stodiesof the lightning performance of unshielded transmission lines by direct strokes, which were made using a developed Monte-Carlo and dynamic travelling wave program. The more important factors affecting the lightning performance as exhibited by the calculations are discussed. This led to the recognition of the basic requirements to achieve good lightning performance for such unshielded lines. A preliminary economical 33kV unshielded line design achieving these requirements is also offered.

Calculation of the Lightning Performance of Unshielded Transmission Lines

A computer program to evaluate the lightning performance of unshielded transmission lines has been developed. The program is based on the Monte Carlo and Dynamic Travelling Wave techniques. It is an improvement over previous methods and includes the simulation of a large number of spans with towers of different insulation characteristics, nonlinearities such as corona distortion, lightning arrester operations , dynamic behaviour of earth connections and multiple flashover assessment of transition from impulse flashover to power arc formation. The program has successfully predicted the lightning outage rate and types of several operating unshielded wood pole lines in Australia.

Computer Methods for the Design and Assessment of the Lightning Performance on Transmission Lines

Available methods for the calculation of the lightning performance of transmission lines are mentioned. To date, statistical methods based on Monte Carlo manipulations of lightning and system data together with the Dynamic Travelling Wave Method of Computation of potentials stressing insulation, appear to be the most sophisticated and indeed provided the most realistic simulations with high accuracy of results. To illustrate the above, a comprehensive computer program based on the two techniques for the calculation of the lightning performance of unshielded transmission lines is described. The program is a major improvement over existing calculation methods as it models the presence of weak-link structures, corona wavefront distortion, change in structure insulation characteristics following flashovers, dynamic representation of resistance of earth connections, lightning arresters, multiple flashover assessment of transition from impulse flashover to power arc formation as well as the use of the electrogeometric method for determining the number of strokes to line. The validity of the program is verified by the successful prediction of the lightning outage rates and types of several operating unshielded woodpole lines.