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:
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.
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.
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.
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.
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.
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.