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Wire & Cable ASIA – September/October 2007
67
Wire & Cable ASIA – January/February 12
The solar cable according to DKE is a two-layer insulated
single core cable with a minimum wall thickness of 0.5mm
in each layer. The most important tests required in this
specification
[2]
are discussed in the following clauses:
4.1 Temperature range
Solar cables according to the German specification
[2]
are
defined for an environmental temperature range from -40°C
up to +90°C. The maximum conductor temperature is
specified at +120°C.
4.2 Hot pressure test
The purpose of this test is to check the mechanical
stability of the cable insulation and jacket under high
thermal and mechanical load. The
test is performed on the completed
cable according to the test method
described in IEC 60811-3-1. Test
temperature is +140°C; the load is
applied for four hours.
4.3 Cold bend test and cold
impact test
Solar plants must be able to work
under extreme weather conditions.
Thus, the components are tested not
only for high temperature but also for
low temperature performance. In the
German specification
[2]
this is taken
into account with high requirements
for the cold bend and cold impact
test. These tests are performed
according to IEC 60811-1-4 at -40°C.
But additionally the cold impact
test is performed with increased
height as well as increased weight of
hammer and intermediate piece.
4.4 Short and long term ageing at
high temperature
A short term ageing test is required
at +150°C with a duration of 168
hours for the insulation as well as for
the jacket material.
Additionally, an Arrhenius test has
to be performed where the materials
have to withstand 20,000 hours at
+120°C (see
Figure 4
). This enables
manufacturers to guarantee a lifetime
of 25 years in the specified operating
conditions.
4.5 Weathering/UV resistance/
humidity
To reveal the performance under
different environmental conditions,
a weathering and UV resistance
test according to HD 605/A1,
part 2.4.20 is required as well as
a damp heat test according to
EN 60068-2-78.
4.6 Dynamic penetration test
A special penetration test was
developed to prove the stability
of the cable jacket and insulation
against mechanical loads. It is
described in Annex E of the dis-
cussed specification
[2]
. As shown in
Figure 3
, a steel
needle is pressed onto the cable sample. The load is
continuously increased until the needle contacts the cable
conductor, indicated by a low voltage electrical circuit.
The load in the moment of contact is derived by a load
cell. This test simulates mechanical loads on the cable
that could be caused by any object or device falling on the
cable or by animals outside.
4.7 Fire performance
Although the danger of fire propagation in outdoor
applications such as solar plants is not a great risk for the
safety of people, a good fire performance is required to
protect the technical equipment.
❍
❍
Figure 1
:
Pressure test at high temperature on the solar cable
❍
❍
Figure 2
:
Hot elongation test