Medium Voltage Application Guide

13678.A
13873.A
Temperature rise
SWITCHGEAR
During short circuit conditions the busbar will rise in temperature, depending on the level of short circuit current and
time duration. This temperature rise must not exceed the thermal limits of any equipment in contact with the
busbar.
Maximum permissible temperature rise for bolt-connected devices, including busbars
Material and dielectric medium
Maximum permissible
temperature (°C)
Temperature rise
above 40 °C ambient
(°C)
Bolted connection (or equivalent)
Bare copper, bare copper alloy or bare aluminium alloy
In air 90 50
In sulphur hexafluoride (SF 6 ) 115 75
In oil 100 60
Silver or nickel coated
In air 115 75
In sulphur hexafluoride (SF 6 ) 115 75
In oil 100 60
Tin-coated
In air 105 65
In sulphur hexafluoride (SF 6 ) 105 65
In oil 100 60
Source: derived from IEC 62271-1
NOTE
When engaging parts with different coatings, or where one part is of bare material, the permissible
temperature and temperature rise shall be those of the surface material having the lowest permitted
value.
Electrodynamic withstand
During short circuit conditions, the peak current associated with the first loop of the fault current produces
electrodynamic forces which stress the busbar and insulator standoff supports. Stress on the busbars must not
exceed the limits of the material used. Bending forces must not exceed the mechanical limits of the insulator
standoffs.
Electrodynamic forces
Busbars (parallel)
Support
I p
I p
e
h =
2
F 1
F
F 1
F 1
l
H
d
d
d Distance between phases (cm) H Insulator height
l Distance between insulators on a single phase
(cm)
h Distance from head of insulator to busbar
centre of gravity
F 1 Force on busbar centre of gravity (daN) F Force on head of insulator stand-off (daN)
I p Peak value of short circuit current (kA)
NOTE: 1 daN (dekanewton) is equal to 10 newtons.
710-12280-00A Medium Voltage Application Guide Page 81