General Cable NZ have been manufacturing medium voltage
XLPE cables for 25 years. We offer products compliant with
AS/NZS4026, AS/NZS1429, BS6622, IEC60502 and designed to operate
at the following system voltages:
| 1900/3300V |
3800/6600V |
| 6350/11000V |
8750/15000V |
| 12700/22000V |
19000/33000V |
Conductors:
Generally Plain Annealed Copper (PAC) and Aluminium (AL)
conductors are used for most applications, but Tinned Annealed
Copper (TAC) can also be supplied where additional protection
from corrosion is required. All conductors supplied are circular
compacted.
Water blocking of the conductors can also be designed into
products. This is achieved by incorporating water swellable
tapes that contain a super absorbent polymer , between the
strands of the conductor. On contact with moisture the polymer
absorbs the water, swells and forms a gel. The gel fills the
interstices of the conductor and acts as a waterblock
restricting the water ingress into the conductor. Super
absorbent polymers give the optimal combination of a quick
swelling reaction and good blocking properties. The water
penetration into the conductor is restricted to a very short
length that remains constant with time, heat or loading cycles.
Insulation:
General Cable uses Monosil technology for MV-XLPE manufacture.
The conductor screen , insulation and insulation screen are
applied in a single triple layer extrusion. This process ensures
smooth interfaces between the insulation and screen materials
minimizing electrical stresses in the insulation.
The silane crosslinking process involves the use of either a
vinyl silane co polymer , or a graft co polymer produced during
the extrusion process by the reaction of a vinyl silane with the
polyethylene insulating material. The final crosslinking occurs
via a hydroloysis of the vinyl silane , followed by a
condensation reaction between hydrolysed silane groups , giving
rise to a crosslinked structure. Crosslinking gives rise to
molecular structure which will not melt of flow under overload
or short circuit conditions.
Silane modification of polyethylene imparts inherent water tree
retardancy to the cable insulation , a Monosil cure can still be
considered a dry cure as the resulting water content of the
insulation is > 250ppm compared to typical CV dry cure water
content of 200ppm.
General Cable only use water tree retardant insulation
materials on MV-XLPE cables, which have passed tests in
accordance with Clause 5.4.8 of Harmonization Document HD605.
S1/S1:1996 Option A.
Screening:
Both copper wire and copper tape screens are offered as design
options. As copper is an expensive material, it is common to
design the screen to match specific installation requirements.
The following technical datasheets offer two screen options
labelled as light or heavy duty. These are defined as
- - Light Duty can safely withstand 13.1 kA for 0.04 second.
- - Heavy Duty can safely withstand 13.1 kA for 1 second.
Where the installation protection system and magnitude of
potential earth faults are known, please contact a company
representative so that we can have the opportunity to design and
offer the most cost-effective solution.
While tape screens are offered, we do not advise their use on
systems greater than 11kV. Swelling of the cable core during
extreme fault conditions may be sufficient to tear the tape and
render it in-operable, and sufficient system protection must be
installed to prevent overloading the cable.
Water blocking of the screen is also available and is achieved
using water swellable tape. This tape is thermally and
chemically stable for the lifetime of the cable and will
withstand the temperature extremes of fault conditions. Water
ingress through a sheath or termination is prevented from
travelling longitudinally, and damage such as corrosion, water
treeing etc is limited to the point of water entry.
Mechanical Protection:
Aluminium Wire Armour (AWA) and Galvanised Steel Wire (GSW) are
offered as standard mechanical protection for single and three
core cables respectively. Non ferromagnetic materials must be
used on single core cables. As the magnetic field travels
through any protection layers on single core cables laid in
trefoil, a ferromagnetic material such as steel will have
significant eddy current losses induced in the wires causing
significant heating of the cable and subsequent de-rating of its
current carrying capacity. The same principle applies when
selecting cable clamps.
General Cable can also provide design services for submersible
installations. Lead sheathing, toredo worm protection and
additional armouring can all be designed and manufactured at the
New Zealand site.
Sheathing:
We offer various sheathing options tailored to suit
environmental and installation conditions, including polyvinyl
chloride (PVC), high density polyethylene (HDPE) medium density
polyethylene (MDPE), and linear low density polyethylene
(LLDPE).
Halogen free, flame retardant and reduced toxicity materials can
also be offered to cater for specific requirements.
Termite protection of cables can also be offered by the
inclusion of an impenetrable nylon sheath, or by the addition of
special additives during the manufacturing process.
Installation:
Cables should never be bent to a small radius. The prescribed
minimums on the relevant data sheet should be considered the
exception rather than the rule and the actual bending radius the
largest which circumstances will permit. A cable must also not
be laid or otherwise bent when it is at such a low temperature
that damage might be caused to the insulation or serving. Where
environmental conditions are at or below 0°C, cable drums will
require heating, or drums stored on a site with a higher ambient
temperature and moved and installed as quickly as possible
before significant cooling can take place.