The Western HVDC Link

For overhead air insulated cables, for AC only consideration of skin depth, and for both AC and DC consideration of corona, tend to be the limiting size determining factors - skin depth drives you to  split the current over multiple thinner strands, to avoid corona you really want a smooth and fat conductor free of any high spots.

intro to the field theories  typical cable sizes    catalog link aluminium and alloy cables for transmission use  Note the comedy names of the common sizes...

Largest practical strands are rated in single figures of kA,  and  that ends  up 30-50mm dia.  There maybe a steel cable in the core of the twist for strength.

Bundles of 2, 4 or very occasionally 6 such cables are commonly seen spaced by spreader bars and dangling off each pylon arm in the UK. Typically the left and right arm triplets are two independent 3 phase circuits, I am not sure how you would split up DC on a standard 6 armed tower.

For overhead air insulated cables, for AC only consideration of skin depth, and for both AC and DC consideration of corona, tend to be the limiting size determining factors - skin depth drives you to  split the current over multiple thinner strands, to avoid corona you really want a smooth and fat conductor free of any high spots.

intro to the field theories  typical cable sizes    catalog link aluminium and alloy cables for transmission use  Note the comedy names of the common sizes...

Largest practical strands are rated in single figures of kA,  and  that ends  up 30-50mm dia.  There maybe a steel cable in the core of the twist for strength.

Bundles of 2, 4 or very occasionally 6 such cables are commonly seen spaced by spreader bars and dangling off each pylon arm in the UK. Typically the left and right arm triplets are two independent 3 phase circuits, I am not sure how you would split up DC on a standard 6 armed tower.