Effect of altitude on audible noise generated by AC conductor corona

[摘要] ENGLISH ABSTRACT: Power utilities are expected to keep the cost of electricity as low as possible. They are alsoexpected to be environmentally friendly and, amongst other things, not to produceunacceptable audible noise. When the electric field on a conductor is high enough corona isproduced and this is accompanied by audible noise. Air pressure, which is directly related toaltitude, has an effect on the voltage at which corona will start. It is more difficult to ionisethe air at sea level (high air pressure) than at high altitude (low air pressure). Altitude doesnot only affect the corona inception voltage, but also the intensity of the audible noise. Athorough scan of literature revealed that there is very little evidence of prior research work onthe effect of air density on corona under fair weather (dry) conditions.In South Africa, transmission lines are built at altitudes higher than 1800 m above sea level.The cost of a 400 kV line is in the region of R2M per km. It is important to predict the noiselevels under a proposed line accurately, before it is energised. This research indicated thatthe altitude correction for conductor corona audible noise, under dry conditions, might besteeper than the general accepted correction of 1 dB/300m. This correction, however,appears to be valid for heavy rain conditions.Under heavy rain conditions the corona is mainly determined by the water droplets, whereasunder dry conditions the condition of the conductor plays the biggest role. The air densitytherefore has a bigger effect on the corona performance under dry conditions. Theimplication of a steeper altitude correction for dry conditions is that too low noise levels willbe predicted for a higher altitude, which could lead to complaints. On the other hand,predictions for lower altitudes will be too conservative.

[发布机构] Stellenbosch University