Electric Power Generation, Transmission, and Distribution

15.2 Main Effects of Corona Discharges on Overhead Lines

(Trinh, 1995b)

Impact of corona discharges on the design of high-voltage lines has been recognized since the early
days of electric power transmission when the corona losses were the limiting factor. Even today,
corona losses remain critical for HV lines below 300 kV. With the development of EHV lines
operating at voltages between 300 and 800 kV, electromagnetic interferences become the designing
parameters. For UHV lines operating at voltages above 800 kV, the audible noise appears to gain
in importance over the other two parameters. The physical mechanisms of these effects—corona
losses, electromagnetic interference, and audible noise—and their current evaluation methods are
discussed below.

Positive Half-Cycle Negative Half-Cycle

V = 38 kV

V = 54 kV

V = 71 kV

V = 98 kV

V = 106 kV

FIGURE 15.7 Corona modes under AC voltage. Electrode: conical protrusion (u¼ 308 ) on a sphere
(D¼7 cm); gap 25 cm;R¼10 kV. Scales: 50mA=div., 1.0 ms=div. (From Trinh, N.G. and Jordan, I.B.,IEEE
Trans., PAS-87, 1207, 1968; Trinh, N.G.,IEEE Electr. Insul. Mag., 11, 23, 1995a.)