Electric Power Generation, Transmission, and Distribution

Figure 14.8is a stress-strain curve (Aluminum Association, 1974) for an all-aluminum 37-strand
conductor ranging in size from 250 kcmil to 1033.5 kcmil. Because the conductor is made entirely of
aluminum, there is only one initial and final curve.

14.3.1.1 Permanent Elongation

Once a conductor has been installed at an initial tension, it can elongate further. Such elongation results
from two phenomena: permanent elongation due to high tension levels resulting from ice and wind
loads, and creep elongation under everyday tension levels. These types of conductor elongation are
discussed in the following sections.

14.3.1.2 Permanent Elongation Due to Heavy Loading

Both Figs. 14.7 and 14.8 indicate that when the conductor is initially installed, it elongates following the
initial curve that is not a straight line. If the conductor tension increases to a relatively high level under
ice and wind loading, the conductor will elongate. When the wind and ice loads abate, the conductor

35,000

30,000

25,000

20,000

Stress, psi

15,000

10,000

5,000

0

.1 .2 .3

Unit Strain, %

Initial Composite

Initial Steel

Final Steel

Final

Aluminum

Final Composite

Initial Aluminum

6 Month Creep1 Year Creep

10 Year Creep

Equations for Curves (X = unit strain in %; Y = stress in psi) :

Initial composite

Initial Steel

Initial Aluminum

Final Composite

Final Steel

Final Aluminum

6 Month Creep

1 Year Creep

10 Year Creep

.4 .5

: X = 4.07 × 10 −^3 + (1.28 × 10 −^5 ) Y − (1.18 × 10 −^10 ) Y^2 + (5.64 × 10 −^15 ) Y^3

Y = −512 + (8.617 × 104 ) X − (1.18 × 104 ) X^2 − (5.76 × 10 −^4 ) X^3

: Y = (37.15 × 103 ) X

: Y = −512 = (4.902 × 104 ) X − (1.18 × 104 ) X^2 − (5.76 × 104 ) X^3

: Y = (107.55 X −17.65) × 103

: Y = (38.60 X −0.65) × 103

: Y = (68.95 X −17.00) × 103

: Y = (68.75 × 103 )X

: Y = (60.60 × 103 )X

: Y = (53.45 × 103 )X

Test Temperature 70 8 F to 75 8 F

FIGURE 14.7 Stress-strain curves for 26=7 ACSR.