Medium Voltage Application Guide

14009.A
SWITCHGEAR
Mechanical strength of busbars
The maximum allowable stress which a busbar can absorb, , is determined by the busbar material.
Maximum allowable values for for different busbar materials
Material Maximum (daN/cm 2 )
Copper ¼ hard 1200
Copper ½ hard 2300
Copper 4/4 hard 3000
Aluminium 1200
Moment of inertia (I) and modulus of inertia (I/V) of busbars
Where:
l = distance between insulator stand-offs on the same phase (cm)
V/I = inverse modulus of inertia for bars of the same phase (cm 3 )
x
x'
x
x'
x
x'
x
x'
x
x'
x
x'
100 x 10 80 x 10 80 x 6 80 x 5 80 x 3 50 x 10 50 x 8 50 x 6 50 x 5
S cm2 10 8 4.8 4 2.4 5 4 3 2.5
m Cu 0.089 0.071 0.043 0.036 0.021 0.044 0.036 0.027 0.022
(daN/cm) A5/L 0.027 0.022 0.013 0.011 0.006 0.014 0.011 0.008 0.007
I cm 4 0.83 0.66 0.144 0.083 0.018 0.416 0.213 0.09 0.05
I/v cm 3 1.66 1.33 0.48 0.33 0.12 0.83 0.53 0.3 0.2
I cm 4 83.33 42.66 25.6 21.33 12.8 10.41 8.33 6.25 5.2
I/v cm 3 16.66 10.66 6.4 5.33 3.2 4.16 3.33 2.5 2.08
I cm 4 21.66 17.33 3.74 2.16 0.47 10.83 5.54 2.34 1.35
I/v cm 3 14.45 11.55 4.16 2.88 1.04 7.22 4.62 2.6 1.8
I cm 4 166.66 85.33 51.2 42.66 25.6 20.83 16.66 12.5 10.41
I/v cm 3 33.33 21.33 12.8 10.66 6.4 8.33 6.66 5 4.16
I cm 4 82.5 66 14.25 8.25 1.78 41.25 21.12 8.91 5.16
I/v cm 3 33 26.4 9.5 6.6 2.38 16.5 10.56 5.94 4.13
I cm 4 250 128 76.8 64 38.4 31.25 25 18.75 15.62
I/v cm 3 50 32 19.2 16 9.6 12.5 10 7.5 6.25
Source: Schneider Electric 2000.
Page 154 Medium Voltage Application Guide 710-12280-00A