International Symposium on Mitigative Measures against Snow ...

<strong>International</strong> <strong>Symposium</strong> on Mitigative Measures against Snow Avalanches
Egilsstaðir, Iceland, March 11–14, 2008
Towers for snow avalanches in 420 kV transmission lines in Iceland
Ragnar Jónsson* and Egill Thorsteins
Linuhönnun Consulting Engineers, Suðurlandsbraut 4a, IS-108 Reykjavík, ICELAND
*Corresponding author, e-mail: ragnarj (at) lh.is
ABSTRACT
This paper describes factors that influenced design and construction of two 420 kV
transmission lines, Fljótsdalslína 3 and 4, in snow avalanche areas in the east part of Iceland.
It presents a description of the snow avalanche loading, the structural solutions and how
assembly and erection was carried out. A total of 83 towers are located in the avalanche prone
areas and requirements to operational reliability of the two transmission lines are high since
they are feeding an aluminium smelter.
1. INTRODUCTION
Landsnet completed the construction of Fljótsdalslína 3 and 4 (FL3 and FL4), two single
circuit 420 kV overhead transmission lines (OHTL) by end of year 2006. The lines will be
operating at 245 kV for the first years. The lines originate at substation Fljótsdalur, close to
the powerhouse of hydropower plant Fljótsdalsstöð, and terminate at Alcoa Fjarðarál, an
aluminium smelter in Reyðarfjörður. The total length of the lines is 102 km, of which FL3 is
49 km and FL4 is 53 km. The lines are located at an elevation of 20 – 620 m above sea level
and lie parallel with 60 m spacing for appr. 80% of the line route. They pass through
challenging areas for transmission lines and were designed for risk of; severe in-cloud icing,
wet snow icing, high wind, snow avalanches, floods, frequent galloping etc. Requirements to
the operational reliability of Fljótsdalslínur 3 and 4 are extremely high as they are the only
transmission lines providing electricity for the aluminium smelter in Reyðarfjörður.
The lines contain a total of 326
towers, of which 83 are located
in areas prone to avalanches.
Of the 83 avalanche towers, 44
are parallel. The phase conductors
consist mainly of duplex
conductors 865-AL3/44-ST4
(dia. = 39 mm, rated strength =
312 kN). In sections with
heavy in-cloud icing, these are
for safety reasons replaced in
FL3 by a simplex conductor
1288-AL3/183-ST4A (dia. =
49.9 mm, rated strength = 604
kN). Earth wires are only
present close to substations and
only 4 towers designed for
avalanche carry earth wires.
Figure 1: Avalanche towers in FL3 in Hallsteinsdalur.
Jónsson and Thorsteins 169