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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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    perspicacious:
    Hmm I had assumed that in normal operation the ring was closed and only opened at two isolators if one (or more than one adjacent) point at the substation required isolation.. 


    Invariably they are operated as mid point open ring to limit fault current ebee.


    Regards


    BOD


    Running open does indeed limit fault current but the main reason is to reduce the number of customers disconnected by a fault.  A closed ring will just trip breakers a both ends on a cable fault unless it has a relatively sophisticated protection scheme which most do not. This protection normally requires circuit breakers rather than switches on the ring which is expensive.  Running open means you only loose half the ring and most supplies can be restored by switching (increasingly using fault passage indicators to identify the faulty section these days).


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  • 0
    perspicacious:
    Hmm I had assumed that in normal operation the ring was closed and only opened at two isolators if one (or more than one adjacent) point at the substation required isolation.. 


    Invariably they are operated as mid point open ring to limit fault current ebee.


    Regards


    BOD


    Running open does indeed limit fault current but the main reason is to reduce the number of customers disconnected by a fault.  A closed ring will just trip breakers a both ends on a cable fault unless it has a relatively sophisticated protection scheme which most do not. This protection normally requires circuit breakers rather than switches on the ring which is expensive.  Running open means you only loose half the ring and most supplies can be restored by switching (increasingly using fault passage indicators to identify the faulty section these days).


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