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Amtech on underground cables

Georgios Papageorgiou
Hi,


Have an issue with amtech and since i'm not an expert , thought I better posted.

Was asked to do some calcs on the AC side of a solar farm but we cant decide on the cables and installation method. 90 deg XLPE is what I used to connect inverters with the main panel, this cable seems to be a 70mm if buried in ducts or 35mm if buried using BICC data. Not sure of the difference between these methods as Amtech describes them identically. 

Also, for the submain, 2 x 240mm single cores per phase seem to handle the roughly 600A load though not sure if this should be PVC or PILC due to the long life cycle of the install.


No site report available for soil conditions therefore assumed the temperature @20C and resistivity @2.5k.m/W

Any input would be appreciated.
  • 0
    Re. BICC data for buried cables, out of interest did you find an answer?

    There is a BICC Cable Handbook available which I'm sure you'd have to refer to in order to distinguish the difference between the two installation methods Amtech describes. Unfortunately I do not have a copy of the BICC handbook, in some instances it appears to form part of Distribution Network Operators (UK) code of practice for underground cable ratings and perimeters.


    Hopefully someone else on the forums can shed more light on the matter as it was something I have come across also.
  • Former Community Member
    0 Former Community Member
    The BICC data assumes half the soil resistivity of the BS7671 data so the cable doesn't get as hot and consequently can carry more current. You can increase the depth of lay to get better CCC as well although this does taper out after an extra metre or so iirc.


    The equipment will die of old age before a buried XLPE/SWA gives out and it gives you an extra 20 degrees of heat to get additional CCC over a PVC 70 degree cable, as long as your switchgear at either end can handle the heat. ProDesign will tell you the max temperature the cable will reach on load if you use the correct report for the cable.
  • 0
    As far as I can tell both methods should be providing the same result as with bicc amtech will just change the rating factors..I've looked at how amtech calcs the bicc method and also manufacturers data for xlpe and the ccc is almost identical so this shouldn't be happening.. 

    I've moved away from bicc since just to be on the safe side

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