The mechanical effects of short-circuit currents in - Montefiore

Figure 3.39 Movement plan view at the center of the left dropper
(Figure 3.37) at the height approximately 7.5m above the
HV terminals.
The diagrams in the Figure 3.38 and Figure 3.39 shows
the movement of the center point of the dropper bundle
at height approximately 7.5 m above the HV terminals
for all three conductors on clashing and the lateral
movement of the pinched conductors, and the separate
movement of the individual conductors for a very short
time after interruption the short-circuit current.
Figure 3.40 Short-circuit force against time curve for the loads on the
disconnector right hand HV terminal.
The maximum loads on the HV terminal of the
disconnector achieved during the short-circuit have been
calculated as:
Right dropper 3.7 kN
Left dropper 3.0 kN
3.4.3. Dynamic behaviour of close and various
degrees of wide bundling
Unlike the close bundling of flexible busbars, which is
not associated with major short-circuit contraction
effects, substantial peak forces due to the contraction of
subconductors occur at the dead end and on the spacers
in the case of wide bundles. Their magnitude and their
eventual static equivalent effect (ESL = equivalent static
load) on support structures and foundations depend,
apart from a number of additional parameters of
configuration and state, as well as of the electrical shortcircuit
data, on the spacing between sub-conductors,
their number and configuration, the stranded conductor
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itself, and the number and the design of the spacers
(rigid, partially or multiply elastic).
Close bundling of multiple conductors, with a spacing
between subconductors approximately equivalent to
conductor diameter, minimizes the direct and indirect
effects of contraction. Up to 400kV this technique is
absolutely viable for substations and has become largely
standard for more recent German installations. This
does not hold true, however, of older plants with wide
bundles, whose reserve potential now needs to be
investigated, nor of stranded conductor arrangements
abroad, where wide bundle spacing as in overhead lines
has been and is the usual technique also in the case
below 400kV. Close bundling is, of course, no longer
feasible with stranded conductors for higher system
voltages.
This section concerns the case A (Figure 1.1) plus B –
long-span horizontal buses connected by insulator
chains to portal structures – where the bus conductors
are twin bundles. The dropper B is connected at
midspan and does not carry current.
The sub-conductor centre line distance is varied from 60
to 400 mm in four individual values.
The following parameters were varied:
- the number of spacers nAH
- the sub-conductor centre-line distance aT
- the short-circuit current duration TK.
The usual practical solution for a close bundle
conductor in Germany is aT ≈ 2 x conductor diameter.
In the case of wide bundling, aT is very much larger.
Figure 3.41 shows the studied arrangement.
M-Portal
N-Portal
Figure 3.41 The studied arrangement fully discretized
The structure is discretized in a full-detail FE model,
using the appropriate beam elements for the framework
of the portals and adjusting the model to achieve first
the proper stiffness and then eigenfrequency values.