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11 KV cables.

broadgage
Until fairly recently, underground 11 KV cables were invariably 3 core, paper insulated, lead covered, with an earthed steel wire armouring. Then came the more modern plastic insulated cables, with earthed armour and a red plastic over sheath to distinguish them from LV cables.


However the modern trend seems to be a bundle a 3 single core cables, each with an aluminium core, plastic insulation, copper wire armouring and a red plastic sheath.

Why is this used ? It seems to me that 3 single core cables would be more costly to manufacture, and more labour intensive to joint or terminate, than one 3 core cable.

I fail to see the advantage, but presume that there must be some advantage, or why make the change ?
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    I think some of the 11kV singles cables use EPR insulation.  They first came a just singles (not pretwisted) and then changed to pretwisted,  I think they are single core for ease of manufacture.  It also helps bending, handling etc. They are much lighter than the old PICAS or lead sheathed variety.  The red fades badly after a few years in some soils so cant be relied on.  Phase is important on rings - there are standards for radials but no way to confirm in most cases.  The non twisted version needs decent trefoil cleats or bands.  There is no armour but there is a [copper] screen.  Care needs to be taken at higher fault levels as the rating of the screen can be exceeded and in some cases with high fault levels this type of cable simply isn't suitable.  IIRC these cables were first used in the mid 1980s in the UK.


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  • 0
    I think some of the 11kV singles cables use EPR insulation.  They first came a just singles (not pretwisted) and then changed to pretwisted,  I think they are single core for ease of manufacture.  It also helps bending, handling etc. They are much lighter than the old PICAS or lead sheathed variety.  The red fades badly after a few years in some soils so cant be relied on.  Phase is important on rings - there are standards for radials but no way to confirm in most cases.  The non twisted version needs decent trefoil cleats or bands.  There is no armour but there is a [copper] screen.  Care needs to be taken at higher fault levels as the rating of the screen can be exceeded and in some cases with high fault levels this type of cable simply isn't suitable.  IIRC these cables were first used in the mid 1980s in the UK.


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