Characteristics of Spatial Distribution for Hum Noise in Ravines under AC Transmission Lines

Experimental Study and Computer Simulation

Abstract

The audible noise which is produced by corona discharge from a transmission line conductor is composed of two major components, namely “hum noise” and “random noise”. Hum noise has a frequency of twice the power line frequency and is generated primarily in rain, fog, and highly humid environments. It is one of the major factors affecting conductor design of transmission lines for voltages above 500kV. In the case of flat ground, hum noise from each conductor bundle generates a complex standing wave near and perpendicular to transmission lines and the statistical characteristics are known. However, recently, bulk transmission lines tend to pass through the hilly areas and cross over ravines frequently. The slopes of the ravines cause multiple reflection of sound waves.
In this paper characteristics of spatial distribution for hum noise level in a ravine are described. The main results are that 1) the rate of increase of spatial mean level of hum noise against the slope of a V-shaped valley is 0.1 dB/degree and 2) the distribution of probability density for hum noise level can be approximately represented by a random walk model based on the random walk theory.