The mechanical effects of short-circuit currents in - Montefiore

d)Methods used
IEC 60865 method :
- Calculation of amplification factor,
- IEC Calculation on the reference case and
application of amplification factor to :
* force on support of rigid conductors (Fd),
* resulting conductor stress (σtot).
Advanced method :
The amplification factor applies, for the
calculation, on the same bases (τ and te) between
the reference case and the considered situation (
for example a three-phase fault on two busbars).
Designers have to determine the bar and the
phase for which the stress is maximum.
e) Examples
Separate Asymmetrical Symmetrical
phase (1) phase (2) phase (3)
d (m) 8.8 2 2
D (m) 4.8 2 2
α -1.186 1.5 0.2
β 1 1.5 -0.750
γ -0.254 0.333 -0.167
φ -25.1° 180° 37.5°
||K|| 1.9 1.167 0.83
ϕmax 132.57° 60° 161.2°
ϕmin 42.57° -30° 71.2°
K 1.8102 1.5556 0.9921
ϕmax
Aster
(4)
132.6° 60°
165°
Kaster
(4)
1.78 1.5552 0.9477
% 1.67 0.02 4.47
Table 2.8 Example of caculation for various structure
types, for three-phases fault on two busbars.
(1) : The maximum response is obtained for a
three-phases fault on two busbars on phase 2 bar
1.
(2) : As for (1), the maximum response is for a
three-phases fault on two busbars on phase 3 bar
1.
(3) : In the case of phase 1 bar 1 and Imono = Itri,
d 3
for < , the maximum response is obtained
D 2
for a three-phase fault on one busbar. For
d 3
> , the phase to earth fault on two busbars
D 2
has the maximum response.
(4) : Results obtained by the Code ASTER.
Given a fault flowing on two busbars, the Code
ASTER of E.D.F. allows one to compute the
influence of the phase variation over the force
applied to the central bar. The results have been
noted on the Figure 2.27, Figure 2.28 and Figure
2.29.
35
Figure 2.27 Separate-phase layout
Force on central bar during a three-phase fault on
two busbars.
Figure 2.28 Asymmetrical associated phase layout
Maximum force during a three-phase fault on two
busbars
Figure 2.29 Symmetrical associated phase layout
Force on outside bar during a three-phase fault on
two busbars.