Electric Power Generation, Transmission, and Distribution

Similar to the case of electromagnetic interference, the ability of the line conductors to produce
audible noise is characterized by the generated acoustic power densityA, defined as the acoustic power
produced per unit length of the line conductor under specific operating conditions. The acoustic
power generated by corona discharges developing in a portion dxof the conductor is then

dA¼Adx (15:16)

Its contribution to the acoustic intensity at a measuring point located at a distancerfrom the discharge site is

dI¼

A

4 pr^2

dx (15:17)

The acoustic intensity at the measuring point is the sum of all contributions from corona discharge
distributed along the conductor:

IRðÞ¼ 2 A

(^1) ð
1
1
4 pðÞR^2 þx^2
dx¼
A
2 R
(15:18)
whereRis the distance from the measuring point to the conductor, and the integral is evaluated in terms
of the longitudinal distancexalong the conductor. Finally, the acoustic intensity at the measuring point
is the sum of the contributions from the different phase conductors of the line
IRðÞ¼
X
j
IjRj

(15:19)
Frequency (Hz)
E 0 = 15.00
E 0 = 16.35
E 0 = 17.80
E 0 = 19.25
E 0 = 20.65
Conductor Bundle 6  1.823 in.
Heavy Artificial Rain: 0 .7 in./h
E 0 : Maximum Conductor Surface Gradient
in kV/cm
Audible Noise Level in dB above 2

. 10

−^5

N/m

2

40

45

50

55

60

65

70

75

80

102 103 104

FIGURE 15.9 Octave-band frequency spectra of line corona audible noise at 10 m from the conductor. (From
Trinh, N.G.,IEEE Electr. Insul. Mag., 11, 5, 1995b; Trinh, N.G. and Maruvada, P.S.,IEEE Trans., PAS-96, 312, 1977.
With permission.)