Why non magnetic material for cable armour

[amaminu]

Our specs say the cable armour shall be of a non-magnetic material. A supplier has proposed using galvanized steel. My company has asked the supplier to replace the galvanized steel with Alum?n?um. S?nce the supplier ?s sourcing the 1x630sqmm 33kV cables from an experienced manufacturer,I believe the use of the proposed galvanized steel is a normal practice.
1) Why should the armour be of a non-magnetic material
2) What is the advantage of Alum?nium over steel?

 

[amaminu]

Since I`m yet to receive a reponse to my post, I will be pleased if someone can g?ve me a link to a previous post on the cable armouring. Thanks

 

[MikeDB]

Running a single phase within a magnetic conduit causes undue heating of the conduit. If all three phases are run within the conduit and loads are balanced, then the heating is minimized.

 

[davidbeach]

Steel armor will be much heavier than aluminum armor.

 

[dpc]

If this is a single-phase cable, magnetic conduit is not an option as mentioned by MikeDB. The steel will quickly get hot due to magnetic field flux exciting a current in the steel. This will generally cause cable insulation failure due to heat.

But I find it hard to believe that a cable manufacturer would even propose such a construction. If it is three-phase, it comes down to cost, weight, durability, etc.

 

[sberbece]

In addition to the advices give above by MikeDb and dpc, I would also suggest you to look at the glands and the gland plated on which the cabled will be terminated.
If you are using single phase cable, then the cable glands and the gland plate shall be of non-ferrous material (usually brass or aluminium), to cancel the magnetic field that will induce currents which will produce heat, and so on…