The mechanical effects of short-circuit currents in - Montefiore

From prior tests the stiffness values are known to be SN
= 1.086 kN/mm, SM = 1.223 kN/mm (Sres = 0.575
kN/mm).
The relevant first eigenfrequencies excited at the
mounted mid crossarm, i.e. next to the suspension
points, are 9 Hz for the N-portal crossarm and 9.5 Hz
for the M-portal crossarm, while the complete portals
have fundamental frequencies of 3 Hz and 4.3 Hz,
respectively. It should be noted that the M-portal stiffer
than the N-portal.
Figure 3.42 Main conductor tensile forces, schematic oscillgraph
0- Static load Fst
1- Contraction maximum Fpi
2- Swing-out maximum Ft
3- Fall-of-span Maximum Ff
The results of the calculations performed on the
structure model of Figure 3.41 are given in the following
[Ref 46].
Figure 3.43 and Figure 3.44 give an example of the
reactions of the support structure upon the short-circuit
of 100 kA – 40 kArms – 0.3 s on the 400 mm bundle
phase conductors with 1 spacer. The comparison of a)
against b) shows clearly the relative reduction of the fast
events – the contraction and the 50 and 100 Hz phenomena
during short circuit. – on the way from the
dead-end fixing point at the crossarm to the bottom end
of the tower (i.e. foundation).
Force
[kN] 80.0
60.0
40.0
20.0
0
0.0 0.4 1.0 1.5 2.0 2.5 3.0
time [s]
Figure 3.43 Exemplary oscillographs of stresses at dead end
55
Force
[103 0.2
kN]
0
-0.2
-0.4
-0.6
0.0 0.4 1.0 1.5 2.0 2.5 3.0
time [s]
Figure 3.44 Exemplary oscillographs of stresses at foundation
Figure 3.45 and Figure 3.46 exemplarily show the
calculated displacements of a bundle conductor for the
same arrangement and short-circuit data as above except
tK=0.1 s at the spacer location and at 1/4 span.
Figure 3.45 Bundle conductor displacement at midspan (position of
spacer)
Figure 3.46 Bundle conductor displacement at 1/4 span (in a location
without spacer)
The first sequence of figures - Figure 3.47 a, b and c -
gives a collection of the calculation results for the
respective tension forces at the dead end in terms of the
recorded maxima Fpi, Ft and Ff for the variants taken