This paper will investigate the technique of modal analysis applied to propagation of signals on overhead transmission lines The propagation problem is first analyzed in phase quantities at a constant frequency and then with modal transformations in the original differential equations From the model analysis, properties of modal transformations are deduced This analysis shows that when earth correction terms are used in the description of the transmission line, the propagation constant matrix can be used to determine the modal transformations; it is also demonstrated that to evaluate the phase quantity results numerically it is necessary to perform a modal (eigenvalue) transformation The general equations, evaluated for perfect earth, show that the surge impedance matrix can be used to determine the modal transformations, as has been done by previous authors

Propagation on Overhead Transmission Lines I-Theory of Modal Analysis

The paper presents an investigation of the electrostatic field of a system of infinitely long parallel cylindrical conductors. Existing analytical techniques can be used only to solve rigorously the field of simple geometries such as a single conductor over a ground plane or inside a grounded cylinder and an isolated two-conductor bundle. Until now only approximate analytical solutions have been obtained for the more practical multiconductor systems; in these, each conductor is represented by a line charge at its center.

Electrostatic Field of a System of Parallel Cylindrical Conductors

The conditions under which corona first occurs for any set of electrodes are an important design consideration since corona can limit the performance of any given configuration of electrical conductors. Here, the 60 Hz ac corona onset voltage for a stranded wire in air is calculated. The criterion involves the characteristics, i.e. composition and pressure, of the gas in which the conductor is immersed and the electric field in the vicinity of the conductor surface. It is found that the calculated corona onset voltage agrees reasonably well with experimental data and that its behavior as a function of overall conductor radius and number of strands is as expected.

Application of a corona onset criterion to calculation of corona onset voltage of stranded conductors

As part of a general study on the possible use of UHV transmission lines in the range of 1200 kV for the James Bay Project, the corona performance of four conductor bundles -6 ×1. 823", 6 ×1. 998", 8 ×1. 63 " and 8 ×1.823"-has been studied in outdoor test cages under conditions of heavy artificial rain and fair weather. The radio interference, audible noise and corona losses of the four conductor bundles have been measured in the test cages, and the corresponding long line levels have been evaluated. The results show that of the four bundles tested the 8 ×1.63" conductor bundle gives the best corona performance. However, ice loading conditions may dictate the use of a six conductor bundle, in which case the 6 ×1.823" conductor bundle seems to give a marginally acceptable corona performance.

A Comparative Study of the Corona Performance of Conductor Bundles for 1200 KV Transmission Lines

The mechanism by which the principal wave, which travels along the line and interferes with radio reception, is generated is expressed in mathematical terms and related to the currents which flow during laboratory tests of samples of conductor. These tests are described in detail. The generating functions so determined are used to calculate the electric and magnetic intensities of the interference field near the line. The statistical properties, namely, the correlation function and the spectral density of the field intensities are employed to superimpose the effects of several line conductors. As an example, a comparison is given of the interference level of two lines equipped with the same conductor but one of horizontal and the other of vertical configuration.

G. E. Adams

Papers

The Calculation of the Radio Interference Level of Transmission Lines Caused by Corona Discharges [includes discussion]

Voltage Gradients on High-Voltage Transmission Lines [includes discussion]

An Analysis of the Radio-Interference Characteristics of Bundled Conductors [includes discussion]