MV design guide - Schneider Electric

Design rules
Busbar calculation
Mechanical busbar strength
c By making the assumption that the ends of the bars are sealed, they
are subjected to a bending moment whose resultant strain is:
F1• l v
η = •
12 I
with
η : is the resultant strain,
it must be less than the permissible strain
for the bars this is:
copper 1/4 hard: 1 200 daN/cm 2
copper 1/2 hard: 2 300 daN/cm 2
copper 4/4 hard: 3 000 daN/cm 2
tin-plated alu: 1 200 daN/cm 2
F1 : force between conductors daN
l : distance between insulators
in the same phase
cm
I/v : is the modulus of inertia
between a bar or a set of bars cm 3
(choose the value in the table on the following page)
v : distance between the fibre that is neutral
and the fibre with the highest strain (the furthest)
phase 1 phase 2
x
c One bar per phase:
b
v
h
x'
I =
I
v
=
b • h 3
12
b • h 2
6
c Two bars per phase:
phase 1 phase 2
v x
b
d
h
x'
I = 2 ( b • h 3
+ S • d 2 )
12
I
v
b • h
2 ( 3
+ S • d 2 )
=
12
1.5 • h
S : busbar cross section (in cm 2 )
xx': perpendicular to the plane of vibration
Check:
η < η Bars Cu or Al (in daN/cm 2 )
28 Merlin Gerin MV design guide Schneider Electric