EXECUTIVE SUMMARY: SHORT CIRCUIT TEST OF GUY WIRES
BACKGROUND OF THE PROJECT
When upgrading Statnetts OHL’s from 300 kV to 420 kV, the distance between phase conductors and
steel guy wires may be reduced in the centre phase of some towers. Consequently the risk of
flashover to these components is increased. However, the present design is not intended to handle
flashovers to and fault current through the guy wires, and thus the idea came up at Statnett to try to
utilize armour rods (no. vernespiraler) to protect the guy wire in the region closest to the conductors.
GOAL OF THE PROJECT
The goal of the project was to identify possible positive effect of armour rods towards arc resistance
of guy wires of steel. Furthermore it was intended to investigate the possibilities of utilizing carbon
fiber rod as guy wire in future tower designs.
GENERAL PROJECT INFORMATION
The project was started in September 2012 and final report delivered in February 2014. Five guy
wires of the type utilised by Statnett were tested. The length of the steel wire was approximately
15 m, and the wire had a cross section of 190 mm2.
One specially prepared sample of a carbon fibre rod intended to simulate a guy wire of this type of
material was provided for test by N-Tec in Norway. The rod was 5 m long and had a square shaped
cross section of 20x20 mm. At the ends, two plates of carbon fibre material had been attached in
order to allow for mechanical connection. All tests were performed at ABB high power laboratory in
Ludvika, Sweden. TRL at the start of project was considered as TRL 2, at the end of the project the
level increased to TRL 5.
R&D METHOD
The guy wire to be tested was strained horizontally 1 m above the floor by approximately 30 kN and
grounded at both ends using cables connected to a steel structure simulating the tower. An arc was
initiated 3 m from one end, at a test current terminal positioned approximately 0.2 m from the wire.
In order to initiate the arc, the terminal was connected to the test object by a thin copper wire. Tests
were performed with different current amplitudes and durations. A summary of the performed tests
is shown in Table 1.
Table 1 Selected test sequence
Test
Date
Object
A
B
C
D
E
F
G
Dec. 18, 2012
Dec. 18, 2012
Dec. 18, 2012
Dec. 18, 2012
Jan. 7, 2013
Jan. 7, 2013
Jan. 7, 2013
Steel, No1
Steel, No2
Steel, No3
Carbon fibre rod
Steel, No4
Steel, No5
Steel, No5 (observe:
same as in test F)
Armour
rod
No
No
Yes
Yes
No
No
Current
[kArms]
15
15
15
15
15
5
10
Duration
[s]
0,2
0,7
0,7
0,7
0,2
0,7
0,7
RESULTS OF THE PROJECT
Tests of steel wires showed that the duration of arc exposure has a great impact on the magnitude of
damages. At tests at 15 kA lasting for 0.2 s, the steel wire without armour rods was burned to a
degree where only a few strands broke. However, at test durations of 0.7 s, a current amplitude of
5 kA was sufficient to damage the bare steel wire resulting in partial breaking. At 15 kA the same
duration resulted in complete breaking of the wire. At the highest stress tested (15 kA and 0.7 s), the
sample without armour rods broke completely, while the sample fitted with armour rods was
damaged to a smaller extent and did not break. Consequently, it can be concluded that there is a
positive effect of armour rods in this application. Under the assumption that selected test durations
are representative, obtained test results indicate that application of armour rods to guy wires does
provide sufficient protection towards damages from arcing and fault current.
The carbon fibre rod did not withstand the test. It more or less exploded due to the heat generated
from the current. Thus, if carbon fibre components are to be utilized in OHL towers, special attention
should be paid to handling of arcs and fault currents.
IMPLEMENTATION OF RESULTS
It is strongly recommended to use armour rod for guy wires when there is a possibility of short circuit
to the guy wires. Conversely the use of carbon fiber rod as guy wire is not recommended for such a
situation.
DISSIMINATION OF RESULTS
The results of this project were documented in the main report delivered to Statnett and have not
been used in any other publication.
Damages to guy wire after test (15.6 kArmss, 0.74 s)
Remainings of carbon fibre rod after test (15.3 kArmss, 0.74 s)