The effect of altitude, temperature and humidity on corona inception and audible noise under HVDC stress

Two investigations were conducted as part of this research. Firstly, the effect of altitude on direct current (DC) corona generated audible noise on overhead conductor was investigated. This was done by evaluating the audible noise performance of a Kingbird conductor at different altitudes in South Africa. Tests were done using a mobile corona cage. Secondly, an investigation into the effect of temperature and humidity on the corona extinction gradient was conducted. These tests were done at a fixed altitude of 1500 MASL. The results for the first aspect show that the correction factor for audible noise was found to be gradient dependent. The correction at lower, more practical gradients, was found to be steeper than the commonly used 1 dB/300 m (for alternating current). It was also noted that for DC corona noise, the single conductor is either quiet or in corona and does not exhibit a gradual transition, as in the alternating current (AC) case. The results for the second aspect indicate that the temperature and humidity have a complex inter-relationship and affect the corona extinction gradient differently. Corona performance is worse during hot and dry conditions for DC voltage, which is opposite to that of AC.