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Armour bonding: Effect on cable rating

Hi all,

Inspired by this recent post (but not wanting to digress too far), the advantage of single-bonding cable is ostensibly the reduced circulating current in the armour and hence increased capacity in the line conductors... But can anyone tell me if there’s a way to quantify this benefit, without recalculating on first principles per IEC60287? Is it as “simple” as calculating the induced voltage using the method in the IET calculations book and then “adding back” the avoided current that would have otherwise ensued to the tabulating rating?

Also I most commonly see this applied at private transformer tails... but surely there they’re normally so short it’s of little benefit unless you’re mainly concerned with fault current rating?

Thanks as always.
Parents
  • Try and keep magnetic an electrical effects mentally distinct.

    'Eddy currents' are electric currents that always want to flow in a direction parallel  to the current that creates them, they create heating in the normal electrical resistance (I2 R) sort of way


    . Magnetic field lines want to form rings around the currents that create them and are the direction that the little atomic scale compasses in the chunk of iron or steel keep trying to swing round to  align with, and generally at 50Hz they more or less keep up, but friction (magnetic hysteresis) means they create some heat doing so.


    When you know which mechanism you are dealing with you know which way things need to be cut or stranded or grouped.

Reply
  • Try and keep magnetic an electrical effects mentally distinct.

    'Eddy currents' are electric currents that always want to flow in a direction parallel  to the current that creates them, they create heating in the normal electrical resistance (I2 R) sort of way


    . Magnetic field lines want to form rings around the currents that create them and are the direction that the little atomic scale compasses in the chunk of iron or steel keep trying to swing round to  align with, and generally at 50Hz they more or less keep up, but friction (magnetic hysteresis) means they create some heat doing so.


    When you know which mechanism you are dealing with you know which way things need to be cut or stranded or grouped.

Children
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