Instantaneous Rainfall Rate: Its Measurement and Its Influence on High-Voltage Transmission Lines

Abstract

When a high-voltage transmission line is exposed to rain there is generally a small amount of corona activity at the surface of the conductors. This activity usually results in a power loss and the generation of audible and radio noise. While the power loss is generally very small compared to the power transmitted, it is possible to measure it on short test lines where no power is carried through the line. It has been found that there are variations in the power loss, and to a lesser extent in the audible and radio noise, during a typical rainstorm. These variations have been ascribed to variations in the instantaneous rainfall rate. An instrument was developed to measure the instantaneous rainfall rate. The results confirm, in fact, that most of the variations in the corona parameters can be attributed to variations in the instantaneous rainfall rate although the relationships are not simply linear. The instrument is described in this paper and some of the results showing the correlation between rainfall rate and the corona loss and audible noise from an ultra-high voltage test line in northern Indiana are presented.