HVAC Corona Current Characteristics and Audible Noise During Rain

Corona Audible Noise is a major factor regarding the public acceptance of overhead lines. In this article, 2-conductor bundle is used to study the influence of rain on AC corona discharge. Rainfall is simulated by a large rain dispenser, which can be adjusted over a wide range. Using this experimental setup, the transient AC audible noise and corona current pulse characteristics under rainfall condition were studied. It was found that there are three different stages of audible noise level during rain, in which the audible noise level during the steady state stage is the highest. This transient characteristic could be explained by two different types of corona discharges for discharges above and below the conductor. Furthermore, the steady state audible noise level was studied under a wide range of rain rates and applied surface electric fields. It was found that the sensitivity of the audible noise level to the rain rate decreases with the applied electric field. This finding is of vital importance as the rain intensity is regarded as one of the most important factors influencing the HVAC audible noise, and a higher rain rate is usually considered to cause a higher audible noise level. A possible explanation of this phenomenon is attributed to the effect of a “critical number of corona sources”, which is well known from DC corona and possible evidence is provided based on long-exposure photos.