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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 ?
  • 0
    In a new British Aluminium smelter in Invergordon, I was an Electrical Engineer for a time. The 4 cell rooms were about 1200m long and because of the VD, had a 415V supply at each end for the busbars to the the overhead crane supplies, fed from 1 of a few ring circuits. The completion of the project required that the final connections of the "ring" were only made to the "crane hospital" bays during the commissioning.stage by a BACO electrician. He connected the phase colours wrongly with the resultant trippimg. I found out then that this chap was colour blind! and could distinguish shades only. He had stated this on his application form for employment but was still recruited.


    I could only keep him in employment, if he agreed to have someone else write down the colours for him. How common is it for a colour blind electrician?, should they be in the trade? would it be seen as discrimination?


    Jaymack
  • Former Community Member
    0 Former Community Member
    20 years ago I re-wired about 15 pubs with a local electrician and we had a routine that whenever someone asked about how we knew which wire was which in the inevitable 24 gang grid switch, I'd tell them that it's even more impressive when you know that my mate is colour blind. They fell for it every time when I explained that the individual cores have very small Braille markings and after a surreptitious look my mate would "feel" the cable and declare it blue, yellow etc to the impressed victim. We even offered to let the enquirer feel the core for himself who announced that, yes, he could feel the marks (in reality, minute extrusion marks). This worked well till we had the Landlord on it who after we'd finished that day, announced his experience to the evening regulars who mercilessly ribbed him for falling for it. He was not a happy bunny with us the next day. so we missed out on teas etc!


    Regards


    BAD
  • 0
    Nice one BAD.

    Reminds me of me old hero Arthur, conspired to trick an apprentice that there was such a thing as a "meat custard" pie/tart thing available from the local bakers. Yes a custard tart with minced beef on top . He`d made one up from damaged stock and got the local delivery guy to "sell" it to him when he requested it one morning.

    Ranks around Long Stand/Sky Hook etc etcmethinks
  • 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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