MV design guide - Schneider Electric

Design rules
Busbar calculation
c Let us fine tune the calculation for θt for Ir = 2 500 A
(rated current for the busbars)
v the MELSON & BOTH equation (cf: page 31), allows us to
deduce the following:
I = constant • (θ-θn) 0.61 et
Ir= constant • (∆θ) 0.61
∆θ = 44.3 °C
I Ir
(θ-θn)
(∆θ)
therefore = ( ) 0.61
2 689
( 2 500 = 50
(∆θ)
)0.61
50
∆θ
2 689
= ( )
2 500
50
∆θ = 1.126
1
0.61
v temperature θt of the conductor after short-circuit,
for a rated current Ir = 2 500 A is:
θt = θn + ∆θ + ∆θcc
= 40 + 44.3 + 4
= 88.3 °C for Ir = 2 500 A
The busbars chosen are suitable because:
θt = 88.3 °C is less than θmax = 100 °C
(θmax = maximum temperature that can be withstood by the parts in
contact with the busbars).
34 Merlin Gerin MV design guide Schneider Electric