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Buried ducts for medium voltage cables

vici
Hello everyone,


Is there any BS or IEC standard indicating typical configurations for multiple ducts buried in the ground? This is mainly in relation to medium voltage cables.


Specifically, I wondered if there was a standard giving guidance on typical arrangements used for multiple ducts to be laid in the ground (e.g ducts arrangement like 3 x 5 or 4 x 4) and backfilling material requirements (e.g. ducts surrounded by concrete or other back fill materials etc..). I am aware of all the minimum depths form the ground level, depending on the conditions (e.g. carriageways, footways, arable land etc..) but I wondered if there were also indications from BS or IEC documents for typical layouts / engineering solutions.


thank you
  • 0
    No, getting out more is overrated, I love such knowledge.


    It also makes my mind wander to other related subjects. For example, London Underground's use of -210 and +420v, giving a total between 'simultaneously accessible parts' of 630v, just below the 650 cut off you mentioned (that I'd forgotten/retconned to 1000v).. is that similarity mere chance, or a way of skirting a higher safety requirement?
  • 0
    Yes, the London underground  voltage is totally arbitrary, actually  the same 630v trains run off 750v where they share track with British rail, and there is a plan to uprate the Metropolitan line to 750V along the full length, as a 250-0-500 DC supply in any case to improve the ohmic loss situation and allow heavier loads on the same network with the same spacing of feed points.

    I think the proposal was to do the Met first, and then the rest a line at a time.


    Actually as heavier loads for vehicle chargers and so on become more common,  as well as considerations of distribution losses move up the environmetal agenda (remember all that Baryonic centre stuff in the last draft of the regs) I rather think we could do to have at least one  additional final distribution  tier  between 690/400 (that is not quite man enough for large loads, and limited to moderate  ranges) and the rather serious 11/7kV that comes with rather too much attendant risk, and the corresponding procedural restrictions about who can use it.

  • 0
    I am not sure if the plug-in power for London Underground trains that they use to move their trains once in depots (which for clear safety reasons wish not to have the rails as  live supply where folk are walking around trains, so they plug into cables on slider rails that run above, and isolate the pick-up shoes) will also be increased to 750V to match, or if the 630v supplies will stay for those short applications - though I imagine any change will be slow, after all each depot already has a local independaant supply anyway.


    Also the regenerative brakes mean that the voltage at the train can be 50 or so volts higher than the nominal line voltage when decelerating. Apparently regenerative braking is not permitted in a few places where there are escalator and lift motors running from the traction circuits - the fear being that if the escalator suddenly speeds up with a jerk as a train brakes to pull in to the station, it may cause injuries. In time all these will be phased out.




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