Original scientific paper
The Possibility of Insulation Level Reduction on 110 kV Overhead Line with Built-in Post Insulators Using Line Surge Arresters
Stane Vižintin
; Elektroinštitut Milan Vidmar, Hajdrihova 2, Ljubljana Slovenia
Ivo Kobal
; Elektroinštitut Milan Vidmar, Hajdrihova 2, Ljubljana Slovenia
Miha Bečan
; Elektroinštitut Milan Vidmar, Hajdrihova 2, Ljubljana Slovenia
Abstract
Installation of line surge arresters (LSA) on overhead lines is normally accomplished with aim of line
performance improvement. Co-ordination insulation procedure carried out during the line design in
most cases doesn't take into account a suppression of overvoltages by using any overvoltage limiting
devices. The decision supported by poor line performance to install LSA is usually made later. The
reduction of overvoltage level depends mainly on the number of LSA installed, but in any case it is
considerable. It means that insulation regarding dielectric strength might this way be over
dimensioned. This fact could be considered for reduction of phase-to-ground and phase-to-phase
distances, which lead to greater level of line compaction. This is of the most importance for lines with
post insulators, since shorter insulators could be used and consequently narrower right of way
achieved. Our target was to investigate the possibility of reducing lightning overvoltages by using
LSA’s attached parallel to the insulators. For the analyses purpose we implemented a mathematical
model of a single-system 110 kV compact overhead line. The Sigma Slp software was used for
computer simulations. The line was investigated from the perspective of lightning over-voltages as
they are the factors the most severely stressing the insulation. We focused to lightning strikes at a
tower top for the case of single-phase (C) LSA installation configuration. The main influencing
parameters were varied such as lightning current, surge shape and tower earthing resistance according
to their most probable values to obtain overvoltage properties. We concluded, that adoption of LSA’s
does not only reduce the overvoltage amplitude in that phase but also changes its shape, which has to
be taken into account for test impulses generation. The physical model of wooden pole with composite
line post insulators was built for testing in high-voltage laboratory. Power frequency and impulse tests
were performed on insulators (phase-to-ground) and between phase conductors (phase-to-phase) in dry
and wet conditions when necessary. Besides standard also non-standard impulse shape tests were
accomplished to obtain withstand voltages for different arching distances. Based on our comparison
with the simulation results we concluded that - speaking in terms of lightning overvoltages - it is
possible to use insulators for the insulation level Um = 72,5 kV (140/325 kV), if LSA’s in phases A, B
and C would be installed. To verify the conclusion in all other respects, further analyses are needed.
Keywords
Compact line; 110 kV; post insulators; overvoltages; insulation level reduction; line arresters; highvoltage laboratory; tests; Sigma SLP; computer simulations
Hrčak ID:
198498
URI
Publication date:
20.6.2017.
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