MV design guide - Schneider Electric

Design rules
Busbar calculation
Let us check
that the chosen busbars
do not resonate.
Inherent resonant frequency
The inherent resonant frequencies to avoid for busbars subjected to a
current at 50 Hz are frequencies of around 50 and 100 Hz.
This inherent resonant frequency is given by the equation:
f = 112
E•I
m•l 4
f : frequency of resonance in Hz
E : modulus of elasticity
for copper = 1.3 • 10 6 daN/cm 2
m : linear mass of the bar 0.089 daN/cm
l : length between 2 supports
or busducts 70 cm
I : moment of inertia of the busbar section
relative to the axis x'x perpendicular
to the vibrating plane 21.66 cm 4
(choose m and I on the table on the previous page)
f = 112 1.3 • 10 6 • 21.66
( )
0.089 • 70 4
f = 406 Hz
f is outside of the values that have to be avoided, in other words
42 to 58 Hz and 80 to 115 Hz:
The solution is OK
In conclusion
The busbars chosen, i.e. 2 bars of 10 • 1 cm
per phase, are suitable for an Ir = 2 500 A and
Ith = 31.5 kA 3 sec.
Schneider Electric
Merlin Gerin MV design guide
37