The mechanical effects of short-circuit currents in - Montefiore

these cases, very low compared to that of phase 1,
loaded at maximum asymmetry in a wind acting
positively with respect to the short-circuit loads. For
the phase to phase fault, the post insulators are not
excited to a maximum level, the risk is reduced by
10% (0.9 equivalent "loaded post insulator"). For the
short circuit hypotheses, there are almost two loaded
post insulators.
Three-phase fault on two busbars
The diagram below shows the relative variation in the
amplitudes of dynamic responses when the phase ϕ is
varied on the 6 bars of a switch bay.
1,0
0,5
0,0
-0,5
-1,0
93
1
0,8
0,6
0,4
0,2
0
0 30 60 90 120 150 180
-0,2
-0,4
-0,6
-0,8
-1
Figure 5.24 Relative variation of the response versus instant of
occurrence of fault and busbars
The ratio d/D is only relevant for faults concerning
two busbars. On the histograms below we note that
the amplitude of loads is smaller compared to the
three-phase fault on a single busbar (reference 1).
Three-phase fault on two busbars D=d three-phase fault on two busbars D=2d
1 2 3 4 5 6
1,0
0,5
0,0
-0,5
-1,0
1 2 3 4 5 6
n (1) ~1 ~1
n (2) 0,5 0,5
Figure 5.25 Relative variation of response at the maximum asymmetry
1) "short circuit" hypotheses
2) short circuit and wind combined hypotheses
In terms of loaded elements, the faults on two busbars
are substantially less stress-generating. The main
contribution is due to the outer post insulators 1 and
6. The ratio d/D has only a minor influence.
5.2.3.7.3. "Separate phases" layout
For this type of arrangement (Figure 2.21), the stressgenerating
fault is the three-phase fault on two
busbars. The diagram below shows the relative
variation in amplitudes of dynamic responses when
the phase ϕ is varied on the 6 bars of a switch bay.
1
0,8
0,6
0,4
0,2
0
-0,4
-0,6
-0,8
-1
Bar 1
Bar 2
Bar 3
Bar 4
Bar 5
Bar 6
0 30 60 90 120 150 180
-0,2
Figure 5.26 Relative variation of the response versus instant of
occurrence of fault and busbars
Bar 1
Bar 2
Bar 3
Bar 4
Bar 5
Bar 6