Altitude Correction Method for Audible Noise of ± 800 kV UHVdc Overhead Transmission Line and its Engineering Application

With the improvement of the voltage level of DC overhead transmission lines (OHTLs), the audible noise (AN) caused by the corona discharge of conductors is an increasingly serious problem. AN has become a critical parameter that determines the selection of conductors, line structures and specifications for UHVdc OHTLs in high-altitude areas. To study the altitude correction method of AN for UHVdc OHTLs, we erected 6 x 720 mm(2) and 6 x 900 mm(2) conductors on DC full-scale test lines located at altitudes of 4,300 m and 50 m, respectively. We carried out an experimental study on AN over a long period and obtained its distribution law at high and low altitudes and its altitude-related increment. At the same time, on four DC reduced-scale test lines located at 4,300 m, 3,400 m, 1,700 m and 50 m above sea level, 6 x 95 mm(2) conductors were erected for experiments. The law that the AN of the DC OHTL shows a nonlinear change with increasing altitude is obtained. Based on the combination of full-scale and reduced-scale tests, an altitude correction method of AN for UHVdc OHTLs considering the influences of both altitude and electric field strength on the conductor surface is proposed. From 0 to 4,300 m above sea level, when the maximum electric field strength on the conductor surface is 19 kV/cm, the increase in AN calculated with the formula suggested by this article is only 55% of the value calculated with the method recommended by the EPRI. The altitude correction formula of AN proposed herein is applicable to the design of UHVdc OHTLs in high-altitude areas, which can greatly save line investment while meeting the requirements of environmental protection.