Electric Power Generation, Transmission, and Distribution

The calculation of ice loads on conductors is normally done with an assumed glaze ice density of
57 lb=ft^3. The weight of ice per unit length is calculated with the following equation:

wice¼ 1 : 244 tDðÞcþt (14:17)

wheret ¼thickness of ice, in.
Dc ¼conductor outside diameter, in.
wice¼resultant weight of ice, lb=ft
The ratio of iced weight to bare weight depends strongly upon conductor diameter. As shown in
Table 14.2 for three different conductors covered with 0.5-in radial glaze ice, this ratio ranges from 4.8
for #1=0 AWG to 1.6 for 1590-kcmil conductors. As a result, small diameter conductors may need to
have a higher elastic modulus and higher tensile strength than large conductors in heavy ice and wind
loading areas to limit sag.

14.1.5.2 Wind Loading

Wind loadings on overhead conductors influence line design in a number of ways:

.The maximum span between structures may be determined by the need for horizontal clearance
to edge of right-of-way during moderate winds.
.The maximum transverse loads for tangent and small angle suspension structures are often
determined by infrequent high wind-speed loadings.
.Permanent increases in conductor sag may be determined by wind loading in areas of light
ice load.
Wind pressure load on conductors,Pw, is commonly specified in lb=ft^2. The relationship betweenPw
and wind velocity is given by the following equation:

Pw¼ 0 :0025(Vw)^2 (14:18)

whereVw¼the wind speed in miles per hour.
The wind load per unit length of conductor is equal to the wind pressure load, Pw,
multiplied by the conductor diameter (including radial ice of thicknesst, if any), is given by the
following equation:

Ww¼Pw

ðÞDcþ 2 t

12

(14:19)

14.1.5.3 Combined Ice and Wind Loading

If the conductor weight is to include both ice and wind loading, the resultant magnitude of the loads
must be determined vectorially. The weight of a conductor under both ice and wind loading is given by
the following equation:

wwþi¼

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

ðÞwbþwi^2 þðÞWw^2

q

(14:20)

TABLE 14.2 Ratio of Iced to Bare Conductor Weight

WbareþWice

ACSR Conductor Dc, in. Wbare,lb=ft Wice,lb=ft Wbare

#1=0AWG-6=1 ‘‘Raven’’ 0.398 0.1451 0.559 4.8

477 kcmil-26=7 ‘‘Hawk’’ 0.858 0.6553 0.845 2.3

1590 kcmil-54=19 ‘‘Falcon’’ 1.545 2.042 1.272 1.6