Low voltage and High voltage power cables


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This paper provides a short exposure on typical small voltage, medium / high voltage cables. The focus is on thermoplastic and thermosetting insulated cables, however, the construction of other cables are similar.

Low Voltage Power and Control Cables

Low voltage energy and control wires are for electrical wires with or below a voltage level of 0.6/1kV.

Conductor:

Copper or aluminium usually trapped. Copper is more dense and stronger than aluminium, but more conductive. Aluminium conductors that are electrically equal have a cross-sectional region about 1.6 times bigger than metal, but they are half the weight (which can save on material costs).

Surface coating (eg. tin, nickel, silver, lead alloy) of copper conductors is common to prevent the insulation from attacking or adhering to the copper conductor and prevents deterioration of copper at high temperatures.

Insulation:

Usually plastics of type thermoplastic (e.g. PVC) or thermosetting (e.g. EPR, XLPE). Mineral insulation is sometimes used, but the building of MI wires is completely distinct from ordinary insulated plastic/rubber wires.

Filler:

Sometimes the interstices of the conductive bundle are filled, usually with a soft polymer material.

Termite Protection

A nylon coat can be implemented for termite safety for subterranean wires, although a bronze phosphorus cloth is sometimes used.

Bedding / Inner Sheath

Typically a compound of thermoplastic (e.g. PVC) or thermosetting (e.g. CSP), the internal cloth is there to hold the package together and provide the cable armour with bedding.

Armour:

For driver package mechanical safety. Typically, steel wire armour or braid is used. To prevent corrosion, tinning or galvanizing is used.

Outer Sheath:

For general mechanical, weather, chemical and electrical protection applied over the armour. Typically a compound of thermoplastic (such as PVC) or thermosetting (such as CSP) and often the same product as bedding.

Usually, the outer cloth is colour-coded to distinguish between LV, HV and instrumentation wires. The numbers and width measurements of the manufacturer are also written on the exterior cloth.

Medium / High Voltage Power Cables:

Conductor:

Copper or aluminium usually trapped. Copper is more dense and stronger than aluminium, but more conductive. Aluminium conductors that are electrically equal have a cross-sectional region about 1.6 times bigger than metal, but they are half the weight (which can save on material costs).

Surface coating (eg. tin, nickel, silver, lead alloy) of copper conductors is common to prevent
the insulation from attacking or adhering to the copper conductor and prevents deterioration of copper at high temperatures.

Conductor Screen:

A semi-conducting tape to maintain a uniform electric field and minimise electrostatic stresses.

Insulation:

Typically a thermosetting for wires below 22kV (e.g. EPR, XLPE) or paper / lead foam. For greater voltages, paper-based insulation is usually used in conjunction with petroleum or gas-filled wires.

Insulation Screen:

A semi-conductive fabric with a feature comparable to that of the driver panel (i.e. electric current monitor).

Conductor Sheath:

Conductive sheath / shield, typically metal or sometimes lead alloy, is used as a cover for keeping electromagnetic radiation in, as well as providing a route for fault and leakage flows (sheaths are grounded at one end of the cord). Lead sheaths are heavier and possibly harder to finish than copper tape, but usually provide greater ability for earth failure.

Filler:

Sometimes the interstices of the conductive bundle are filled, usually with a soft polymer material.

Termite Protection:

For underground cables, a nylon jacket can be applied for termite protection, although sometimes a phosphor bronze tape is used.

Bedding / Inner Sheath:

Typically a compound of thermoplastic (e.g. PVC) or thermosetting (e.g. CSP), the internal cloth is there to hold the package together and provide the cable armour with bedding.

Armour:

For driver package mechanical safety. Typically, steel wire armour or braid is used. To prevent corrosion, tinning or galvanizing is used. Also used when metal armour is not permitted is phosphor silver or tinned metal weave.

Outer Sheath:

For general mechanical, weather, chemical and electrical protection applied over the armour. Typically a compound of thermoplastic (such as PVC) or thermosetting (such as CSP) and often the same product as bedding.

Outer sheath is normally colour coded to differentiate between LV, HV and instrumentation cables. Manufacturer’s markings and length markings are also printed on the outer sheath.